The Underlying Mechanisms between Customer Incivility and Employee’s Response: A Systematic Literature Review

Past studies have been conducted on the consequences of customer incivility toward frontline employees, but not much is known about the underlying mechanism, that is, what mediates or moderates frontline employee’s response towards customer incivility. It has been challenging to perform a systematic review on this research topic because previous studies did not include the review procedures, hence presenting a substantial challenge for other researchers to interpret or replicate. Therefore, the aim of this study is to conduct a systematic literature review of the extant literature focusing on frontline employee’s response due to customer incivility. The review was conducted following five key methodological steps, which are guided by ROSES as the review protocol. The process included formulation of research questions, followed by utilizing the systematic searching strategies (identification, screening, and eligibility) on two main and two supporting databases namely Scopus, Web of Science, Google Scholar, and Dimensions. Next, quality appraisal of the articles was performed and data extraction using thematic analysis approach was conducted on 26 articles that were systematically selected for this review. The analysis generated 44 variables and 15 sub-themes as the underlying mechanisms of the employee’s response to customer incivility, which are further grouped into two main themes: 1) personal factors; and (2) situational factors.


Introduction
The interaction between customers and employees is important in successful business transactions.However, the interaction is not always pleasant for the employees.One of the problems that they could encounter is customer incivility.It is defined as low-intensity deviant behaviour, perpetrated by someone in a customer or client role, with ambiguous intent to harm an employee, in violation of social norms of mutual respect and courtesy (Sliter et al., 2010).Previous studies have shown customer incivility has detrimental consequences on employee well-being (Arnold & Walsh, 2015;Kim & Qu, 2019), employee intrinsic motivation and service performance (Yoon, 2020), and rating of customer service quality (Sliter et al., 2010).Of all the employees in an organization, frontline employees are directly affected by customer incivility.It is because of the job nature that requires them to interact with the customers on a frequent basis; thus, they are more likely than other employees in the same organization to experience incivility instigated by customers.
According to Sliter et al (2012), 70 percent of frontline employees are affected by uncivil customers, and this has increased to 98 percent in a study done by (Kim and Baker, 2019).Frontline employees may not face many difficulties to express their true emotions and behaviour during positive interactions with the customers.However, they will find it more difficult if they need to face uncivilized customers.In the incivility literature, the emotions and behavioural-related issues associated with frontline employees have been widely discussed, which most of it has revealed negative outcomes for employees.Scholars had addressed the effect of customer incivility on emotional labour (e.g., Szczygiel & Baziriska, 2021;Zhan et al., 2021), emotional exhaustion (e.g., Alolaa et al., 2019;Yang et al., 2020;Yoon, 2020;Yue et al., 2020), emotional intelligence (e.g., Szczygiel & Baziriska, 2021), revenge motivation and service sabotage (Cheng et al., 2019); lower service levels to uncivil customers (Frey et al., 2019); employee revenge (Huang et al., 2018); rumination (Boukisa et al., 2020); and turnover intentions (Alolaa et al., 2019;Melhem et al., 2019).Most of the research in the literature examines negative outcomes to show how severe the issue is, but recent research also demonstrates that customer incivility could lead to numerous positive outcomes.Similarly, moderators and mediators are found to mitigate the adverse effects of customer incivility (Sliter et al., 2010).Since then, individual attempts have been made by scholars in exploring the possible mediators and moderators that could explain the relationship between customer incivility and the frontline employees' responses.
A systematic literature review study on the underlying mechanisms between customer incivility and employee's response is worth because it revealed the positive and negative impacts triggered by customer incivility in one study.Since customer incivility is an important issue to focus on and a very costly problem, appropriate actions and strategies should be taken to reduce the damage and turn it into a positive outcome.Furthermore, the results from systematic literature review will provide employers, supervisors, and management with insight into how they can guide employees toward positive behaviour when they perceive incivility as a stressor.This new insight will assist employers to create awareness, prepare employees to face demanding customers and change the current impression of incivility overall.

Research Gap
The impact of customer incivility on frontline employees has been the focus of a significant number of empirical studies.The empirical studies had all been supported and justified by traditional literature reviews.However, most literature reviews in the management field follow a narrative rather than a transparent methodology, hence they are not systematic by nature (Briner & Denyer, 2012).They also mostly used samples that were not representative and procedures that were not systematic (Oakley, 2002).Traditional literature reviews usually skip the evaluation of the quality of articles and omit contradicting studies because of their biased intention to support the hypothesis that the authors had developed.Hence, because of the lack of systematization and transparency, traditional literature reviews are quite likely to create more biases (Kraus et al., 2020).This article sought the use of systematic literature review (SLR) to perform an analysis comprehensively on the role of underlying mechanisms in customer incivility towards frontline employees.SLR has more advantages compared to traditional literature review because SLR is a specific methodology that enables a whole article to be created based on the review of the literature without collecting empirical data.According to Kraus et al (2020), an SLR means a review of an existing body of literature which had used transparent and reproducible methodology in searching, assessing its quality, and synthesizing it, with a high level of objectivity.Therefore, a systematic literature review is one of the methods employed in reviewing existing literature in a more systematic manner (Shaffril, 2020).
To conduct a systematic review, the process includes an orchestrated search of literature that is targeted to address a particular question or issue that has been determined and developed.The literature identified is then analyzed and synthesized using methods that are methodical, logical, and transparent.Hence, the conclusions and implications that are derived from this process are well-grounded in the literature studied.In other words, a highquality systematic review is so much more than a mere exercise in locating, charting, or tallying literature, even in a rigorous manner.Such reviews (e.g., keywords used, articles selection) require the ability to recognize the significant points as well as to synthesize and communicate the importance of the findings in an articulate and proper manner (Alexander, 2020).
Even though some studies attempt to review the issue of the impact of customer incivility on frontline employees systematically, less focus has been given to the underlying mechanisms of the relationship between customer incivility and frontline employees' response.Little is known about the factors that might moderate and/or mediate such a relationship, which leads to a lack of understanding of the negative and positive chain of customer incivility in a systematic way.This review is guided by the central research question: What are the underlying mechanisms between customer incivility and the frontline employee's response?This study aimed to fill the gap by reviewing previous related studies systematically on the underlying mechanism of the relationship between customer incivility and reaction outcomes among frontliners.Although customer incivility and its consequences have been studied by many scholars, there is no study so far that has integrated the various single studies into a comprehensive study in understanding these underlying mechanisms.Furthermore, only one study has adopted the systematic literature review in relation to customer incivility.The study, however, focuses on the impact of customer incivility on the service provider.Therefore, the current study aimed to identify the potential underlying mechanism that may mitigate and/or exacerbate the negative response of frontliners following experiencing customer incivility using a systematic literature review.

The review protocol -ROSES
This study utilized the Reporting Standards for Systematic Evidence Syntheses or ROSES as the protocol for the review.ROSES was developed by Haddaway et al (2018) for review of conservation and environmental management literature due to several limitations related to PRISMA or the Preferred Reporting Items for Systematic Reviews and Meta-Analyses by (Liberati et al., 2009).Therefore, ROSES was adopted for this study.It is useful as a methodological guidance as well as a reporting standard in comparison to PRISMA, which is more of a checklist rather than a comprehensive processual guide (Haddaway et al., 2018).In addition, PRISMA is more suitable for studies that are related to health and medicine (Haddaway et al., 2018), which are fundamentally different from other fields of studies, especially social sciences (Shaffril et al., 2020).
Based on ROSES, the process of SLR for this review began by designing the appropriate research question.Then, the systematic searching strategy was applied, which comprises three key sub-processes namely identification, screening (with inclusion and exclusion criteria) and eligibility.Then, the appraisal of quality of articles was conducted to ensure that only articles of quality are included for review.Finally, the method of extracting the data for the review and its analysis and validation were described.

Formulation of Research Questions
The research question for this study was formulated using PICo worksheet, a tool designed to help researchers to develop appropriate research questions for the purpose of review by defining the Population or Problem, Interest and Context of the study (Lockwood et al., 2015).For this study, the authors have determined 'customer incivility' as the problem, 'underlying mechanism' as interest and frontline employees as the context; which guided the authors to formulate the main research question: What are the underlying mechanisms between customer incivility and employee's response?

Systematic Searching Strategies
The systematic searching strategies involve three main processes which are identification, screening, and eligibility.

Identification
Identification is a process to comprehensively identify the synonyms, related terms, and variations for the main keywords for the study which are customer incivility, frontline employee, emotional and behavioral response.This method intends to provide more options for the selected database to search for more related articles for the review.The keywords for this study were developed based on the research question, as proposed by (Okoli, 2015).The keywords were further enriched by adding synonyms and alternative terms based on our search in thesaurus dictionaries, keywords suggested by the experts in fields, keywords used by past studies, and keywords suggested by the two main database search engines namely Web of Science (WoS) and Scopus.
Whenever appropriate, the combination of keywords and alternative terms such as 'affective event', 'emotion-rule dissonance', 'emotional dissonance', 'emotion regulation', 'emotional regulation', 'emotion display', 'emotional display', 'emotional state' and 'emotional labor' as well as other specific-emotional labor such as 'deep acting' and 'surface acting' as well as 'behavioral response' and 'behavioral reaction' were submitted through functions of phrase searching and Boolean operator (OR, AND).To ensure the accuracy of the search, alternatives of the terms 'customer' and 'incivility' were entered separately where alternatives for incivility such as mistreat*, rude*, discriminant*, disrespect*, impolite*, offen*, insult*, unkind, "lack of regard", uncivil*, violat*, insensitiv*, unruly and others.Patient, patron, client, and student were also included as alternative terms to 'customer' because they are included among the common contexts of past studies on customer incivility.
The full search string for advanced searching in the main databases was developed based on Boolean operator, phrase searching, truncation, wild card, and field code functions (Table 1).Cooper et al (2018); Hayrol (2020) had encouraged diverse searching strategies; rigorous searching, to extend the search, and to ensure a wide coverage.Thus, manual searching strategies, namely handpicking techniques were applied for the two supporting databases Google Scholar and Dimensions.The main keywords were also used for the search of the articles in the databases.

Table 1
Search strings used in the primary databases Database String Scopus TITLE-ABS-KEY (("emotional labo?r" OR "affective event" OR "display rule" OR "emotion-rule dissonance" OR "emotional dissonance" OR "emotion regulation" OR "emotional regulation" OR "emotion display" OR "emotional display" OR "emotional state" OR "deep acting" OR "surface acting" OR "behavi?r* response" OR "behavi?r* reaction") AND (customer OR client OR patron OR patient OR student) AND (incivility OR mistreat* OR rude* OR discriminant* OR disrespect* OR impolite* OR offen* OR insult* OR unkind OR "lack of regard" OR uncivil* OR violat* OR insensitiv* OR unruly) AND ("frontline employee" OR frontline* OR staff OR worker OR "front desk" OR concierge OR "front office" OR "customer-contact" OR front-line* OR reservation OR "front-office" OR "service employee" OR "service worker" OR "service staff")) Web of Science (WoS) TS = (("emotional labo?r" OR "affective event" OR "display rule" OR "emotion-rule dissonance" OR "emotional dissonance" OR "emotion regulation" OR "emotional regulation" OR "emotion display" OR "emotional display" OR "emotional state" OR "deep acting" OR "surface acting" OR "behavi?r* response" OR "behavi?r* reaction")) AND (customer OR client OR patron OR patient OR student) AND (incivility OR mistreat* OR rude* OR discriminant* OR disrespect* OR impolite* OR offen* OR insult* OR unkind OR "lack of regard" OR uncivil* OR violat* OR insensitiv* OR unruly) AND ("frontline employee" OR frontline* OR staff OR worker OR "front desk" OR concierge OR "front office" OR "customer-contact" OR front-line* OR reservation OR "front-office" OR "service employee" OR "service worker" OR "service staff")) Regarding the choice of databases as the sources for the present review, the two leading databases, WoS and Scopus, were chosen due to their strengths and advantages.First, they can provide advanced search functions for their comprehensive collections of over 5000 indexed publishers.Articles from WoS and Scopus are also preferred due to the databases' good reputation in controlling the quality of the articles', and considered as reputable sources across multi-discipline research, including management studies (Martin-Martin et al., 2018;Gusenbauer and Haddaway, 2019).
The selection of Google Scholar as one of the supporting databases is in line with the suggestion made by Haddaway et al (2015) who noted the advantages of Google Scholar to act as a supporting database in a systematic literature review process.First of all, it is the most comprehensive free source of publication and citation data and able to yield a large number of results -according to Gusenbauer (2019), 389 million are documents available in this database.Furthermore, Google Scholar's search engine performs well in retrieving scholarly items, including those that are indexed by established publishers, compared to other discovery tools (Loan and Sheikh, 2018).In addition to Google Scholar, we included Dimensions as another supporting database, following Harzing (2019) who reported that is has a similar or better coverage for both publications and citations, although with significantly lower coverage than Google Scholar.If our findings can be confirmed by larger-scale studies, it can be established that Dimensions does serve as a good alternative to Scopus and the Web of Science for both literature reviews and citation analysis.
A total of 281 relevant articles were found after the initial searching process was conducted in these four databases namely Scopus, Web of Science, Google Scholar, and Dimensions.This number was finally reduced to 26 articles ready for the analysis after the process screening, eligibility and quality appraisal was performed.

Screening
This study screened all the 281 initial articles by defining the criteria for article selection which was automatically considered based on the sorting function available in the database.The selection criteria were based on the research question, as proposed by Kitchenham and Charters (2007).It is quite impracticable for the authors to review all the published articles that exist, therefore Okoli (2015) proposed that researchers should decide on the range of period that they would be able to cover.On the other hand, Higgins, and Green (2011) stated that restriction on timeline publication should be employed only if it is established that related studies could only have been reported during a specific time period.Based on our initial screening, it was noticed that the number of studies related to customer incivility towards front liner employees have begun to surge in the 2010s.Therefore, the year 2010 was set as the beginning of the timeline included in this review.
The decision to limit the search up to 2021 publications was made because the searching process had only started in Feb 2022 and the year have yet to end.Thus, based on this reason, the timeline between 2010 and 2021 was selected as one of the inclusion criteria.Further, to ensure the quality of review, only articles with empirical data and that are published in journals were included.In addition, only articles published in English are included in the review to prevent confusion or the need for translations.This process had excluded 139 articles (including two articles in languages other than English) as they did not fit the inclusion criteria and removed 24 duplicated articles.The inclusion criteria were applied by reviewing through auto-screen articles that are aligned with the research objective which are articles that focus on customer incivility.The remaining 118 articles were used for the third process: eligibility.

Eligibility
Eligibility is the third process where the authors manually inspected the articles retrieved to make sure that all the remaining articles (after the screening process) meet the criteria as outlined.This process was executed by reviewing the title and abstract of the articles.According to Xiao and Watson (2018), there is no single one database that is perfect.Thus, manual screening is needed to ensure that all articles included for this review are relevant to answer the research question that has been determined.At the stage of screening the titles, a total of 44 articles had been omitted, while a further 37 articles had been excluded at the stage of screening the abstracts.After the content of the shortlisted articles had been read by the authors, nine articles were removed.Altogether, this process excluded 90 articles due to the focus on underlying mechanism between customer incivility and the outcome.Overall, only 28 articles were selected for the quality appraisal.

Quality Appraisal
In order to establish that the methodology and analysis of the chosen studies had been performed correctly, a quality appraisal step had been conducted using the Mixed-Method Appraisal Tool (MMAT) by (Hong et al., 2018).Using MMAT, researchers are able to appraise a systematic mixed studies review and conduct the appraisal of five kinds of studies which are quantitative descriptive studies, qualitative research, randomized controlled trials, nonrandomized studies, and mixed methods studies (Hong et al., 2018).Two screening steps were performed for each study that had been selected before the researchers proceeded to the quality assessment.Using five main criteria that had been established in the research design, assessments were performed on the chosen articles based on their quality.MMAT assisted in focusing on criteria such as the appropriateness of the research questions to provide adequate data, the adequacy of qualitative data collection to address the research questions, the coherence between qualitative data sources, data collection, analysis, and interpretation, in order to ascertain that the qualitative sources chosen had a sound methodology and had undergone rigorous analysis.Table 3 shows the questions that we use for quality appraisal

Table 3 Mixed Methods Appraisal Tool (MMAT), version 2018
Category of study designs Methodological quality criteria Screening questions (for all types) S1.Are there clear research questions?S2.Do the collected data allow to address the research questions?Further appraisal may not be feasible or appropriate when the answer is 'No' or 'Can't tell' to one or both screening questions.
1. Qualitative 1.1.Is the qualitative approach appropriate to answer the research question?1.2.Are the qualitative data collection methods adequate to address the research question?1.3.Are the findings adequately derived from the data?1.4.Is the interpretation of results sufficiently substantiated by data?1.5.Is there coherence between qualitative data sources, collection, analysis and interpretation?

2.
Quantitative randomized controlled trials 2.1.Is randomization appropriately performed?2.2.Are the groups comparable at baseline?2.3.Are there complete outcome data?2.4.Are outcome assessors blinded to the intervention provided?2.5 Did the participants adhere to the assigned intervention?3. Quantitative nonrandomized 3.1.Are the participants representative of the target population?3.2.Are measurements appropriate regarding both the outcome and intervention (or exposure)?3.3.Are there complete outcome data?3.4.Are the confounders accounted for in the design and analysis?3.5.During the study period, is the intervention administered (or exposure occurred) as intended?

4.
Quantitative descriptive 4.1.Is the sampling strategy relevant to address the research question?4.2.Is the sample representative of the target population?4.3.Are the measurements appropriate?4.4.Is the risk of nonresponse bias low? 4.5.Is the statistical analysis appropriate to answer the research question? 5. Mixed methods 5.1.Is there an adequate rationale for using a mixed methods design to address the research question?5.2.Are the different components of the study effectively integrated to answer the research question?5.3.Are the outputs of the integration of qualitative and quantitative components adequately interpreted?5.4.Are divergences and inconsistencies between quantitative and qualitative results adequately addressed?5.5.Do the different components of the study adhere to the quality criteria of each tradition of the methods involved?Source: Hong et al (2018) For this quantitative research design, assessment criteria such as the relevance of the sampling strategy towards the research questions, the sample's representativeness to its population, the appropriateness of the measurement, and the suitability of the analysis performed were applied by the authors.As for this mixed-method research design, using MMAT had helped to provide guidelines concerning the rationale for using the mixed-method to address the research questions, the effectiveness of the different research design to answer the research questions, the integration of qualitative and quantitative, and the ability to address divergences and differences between research designs to control the quality from the methodological and analysis perspectives.
Then the corresponding author evaluated the methodology and analysis processes of each article with the help from the two co-authors.The authors had perused each article thoroughly by focusing on the methodology and analysis chapters.The authors inspected each article using the MMAT guidelines, such as checking for the consistency of the sampling performed and analysis undertaken (e.g., random sampling vs. inferential analysis) (see Table 3).All the articles were evaluated based on five criteria with three options given to indicate the results which are: "yes", "no", and "don't know/can't tell".If an article met three or more criteria, it was accepted for use in the review.All assessment decisions were made on mutual agreement, and any disagreement was settled quickly via discussion among the authors.Based on these steps taken, all authors agreed that all selected articles had passed the minimum quality requirement with regard to the methodology and analysis sections.In total, 15 articles fulfilled all criteria, seven articles fulfilled at least four criteria, and a further four articles managed to fulfil at least three criteria as tabulated in Table 3.Therefore, this study proceeds with 26 articles for data extraction and analysis.

Data Extraction and Analysis
Since the review depended on diverse research designs, the best method to integrate the differences was by conducting qualitative synthesis after the articles had been thematically analyzed (Whittemore & Knafl, 2005).From a few options of qualitative syntheses, this study review has chosen to apply the approach proposed by Flemming et al (2019), who focused on the suitability of thematic synthesis on synthesizing data from diverse research designs, because of its flexible mode.Thematic analysis is a type of analysis which undertakes the steps in determining and distinguishing the patterns of selected studies by identifying any similarities or relationships that might be present in the studies (Braun and Clarke, 2019).In this study, the thematic synthesis was performed by applying the processes proposed by (Kiger and Varpio, 2020).
Firstly, the authors read the whole dataset actively and repeatedly to familiarize themselves with it.This step had presented the authors with valuable orientation to the raw data and set the foundation for all subsequent steps.
The second step was to generate initial codes.In this process, the data as organized at a granular and specific level.For this step, all selected articles were read by the authors and all data that are related to the main research question was extracted.
Next, the third step comprised theme generation.The synthesis depended on an inductive coding framework by deriving the themes from the coded data.Inductive coding frameworks was applied and any interests, similarities, and connection between the extracted data were noted based on the coded data.The themes derived were associated with the original data and they reflected the whole dataset (Braun & Clarke, 2019).
The process flow of the selection of articles for SLR performed in this study, from identification to data extraction and analysis, is summarized in Figure 1.

Descriptive Analyses of Selected Articles
The past few decades have seen increasing attention in studies on customer incivility in many leading academic journals published by reputable publishers such as SpringerLink, Taylor & Francis, ScienceDirect, Emerald Insight, Intercedence Publishers, Wiley Online Library and SAGE Publications.This section discusses how the body of knowledge in the area of customer incivility has developed over the years by reviewing the literature on the focus area of customer incivility, sources of articles, year of publication and the methodologies used in the past studies.

Sectors of Service Studied in the Literature
As the present study purposely focused on frontline employees, all articles included in the review feature several sectors related to service sectors and the related nature of jobs that require employees to interact with customers.A big portion of past studies was in the retail sector (19.2% or 5 out of 26 articles), followed by food and beverages (particularly restaurants), and healthcare (particularly hospital nurses).There was one article each that studied the employees in the context of public service and telecommunication.Most of the articles (30%), however, did not specify the contexts of the study but the focus was on the frontliners across sectors.Figure 2 breaks down the percentage of the articles published according to their contexts.2) and Journal of Applied Psychology (2), followed by others.This shows that customer incivility has been a subject of research across a spectrum of journals, with the majority of them in the area's hospitality and psychology.Figure 3 shows the top eight journals with their respective number of articles published.
Figure 3: Sources of Articles

Years of Publication
This review included the articles published within the timeline of the year 2010 to 2021 only.The earliest article post-2010 that mentioned employees' response to customer incivility was written by Grandey et al. in 2012.For the next two years, it was the only relevant article published on this topic.After this hiatus, the research interest began to surge in 2015 with three publications; and the trend remains relatively positive since.Eight more articles were published between the period of 2016 to 2019 (two each in 2016 and 2017, one article in 2017 and three articles in 2019).During this initial period of conception of customer incivility as a research interest, it is noted that the number of publications is scant.However, the interest peaked in the two most recent years of 2020 and 2021, with eight and six articles published in these two years respectively.This surge in the number of articles could be indicative that the topic of employees' response to customer incivility, particularly ones that focused on emotional and behavioural response as the underlying mechanisms, has now piqued the interest of researchers.

Methodologies Used in Past Studies
Various types of methodology have been employed in the research of customer incivility.Four research approaches of surveyed journal articles have been identified by the present study, which is the conceptual, quantitative, qualitative, and mixed-methods.Conceptual method analyses the concepts and models as well as research gaps from the previous literature.A quantitative study empirically investigates the factors of underlying mechanisms in mitigating or escalating the consequences of customer incivility at both personal and situational levels.Meanwhile, a qualitative study presents an analysis of customer incivility using a case study, interview, or observation.Finally, a study that combines both quantitative and qualitative approaches is defined as a mixed-method study.
Figure 5 shows the distribution of methodologies in customer incivility studies.The figure clearly shows that quantitative research was the primary methodology used to investigate customer incivility during the period included in this review (24 out of 26 papers) and the survey was the most popular quantitative method.Researchers have also used other methodologies, but the use of the qualitative method and mixed-method for customer incivility studies remains very limited.This trend seems to indicate an emphasis on empirical research.However, it is possible for future studies to conduct more qualitative/explorative research on underlying mechanism of customer incivility.

Themes and Sub-themes
The thematic analysis of the articles included in this review generated two major themes, namely 1) personal factors and 2) situational factors.These themes were derived from the variables that constitute the underlying mechanisms of the relationship between customer incivility and the reaction outcomes of the frontline employees as discussed in existing research.The sub-themes generated from our analysis of the variables found in the literature include ability, affect, perception, attributes, personality, and cognitive reappraisal, which we further categorized into personal factors.Whereas the sub-themes related to the situational factors are job control (Park & Kim, 2018), organizational climate (Mattar, 2021) transformational leadership (Arnold & Walsh, 2015) and supervisor and organizational support (Richard et al., 2016, Cho et al., 2016).Table 4 tabulates the variables, themes and sub-themes generated from this study.

Ability
Research has identified moderating and mediating factors that can buffer or exacerbate the negative impacts of customer incivility.Employee abilities such as job meaningfulness and perspective taking (Arnold & Walsh, 2015), recovery self-efficacy (Park & Kim, 2018), emotional intelligence (Szczygiel & Bazinska, 2021), resilience (Nguyen & Besson, 2021), and emotional regulation (Cho et al., 2016) are among the factors that influence the relationship between customer incivility and frontline employees' response.Ability refers to the relatively stable capabilities that individuals must enable them to perform a range of activities, be it cognitive, emotional, or physical (Colquitt & Colquitt, 2019).It is one of the personal characteristics that are a function of both genetics and the environment.As such, apart from being an inherent characteristic, a person's learning, education, and other experiences play a role in determining their abilities; that translates into how they respond either positively or negatively to a particular situation, including customer incivility.For example, job meaningfulness and perspective taking did not moderate the relationship between customer incivility and employee wellbeing (Anorld & Walsh, 2015), implying that employees who are subjected to customer incivility will continue to have a negative impact even if their job is meaningful to them.On the other hand, factors such as recovery self-efficacy (Park & Kim, 2018), emotional intelligence (Szczygiel & Bazinska, 2021) and resilience (Nguyen & Besson, 2021) are identified to mitigate the adverse effects of customer incivility on employee's emotions and behaviours.

Affect
In a service organization, ensuring continuous improvement in services provided by frontline employees to customers is a necessity since they are dealing directly with customers on daily basis.On the other hand, frontline employees are in a stressful and perplexing scenario in which they must satisfy both the corporation and the customers at the same time especially when they are facing customers' incivility.Thus, the presence of underlying mechanisms is crucial in ensuring that frontline employees can mitigate the negative response.
However, based on the analysis of the articles, most of the underlying mechanisms that can be categorized under effects such as emotional exhaustion, anger, negative affect, burnout, emotional dissonance, and work meaningfulness had escalated the negative responses.For example, customer incivility has a negative effect on frontline employees' behaviours since the negative treatment displayed by a customer is sequentially double mediated by frontline employees' surface acting and emotional exhaustion (Hur et al., 2015).In addition, frontline employees who experienced more customer incivility will perceive their work to be less meaningful and experience more emotional dissonance, which consequently will reduce their job satisfaction (Qi et al., 2020).
On the contrary, customer-based perspective-taking can be a viable intervention and training tool to empower frontline employees when facing customer incivility and will decrease the negative affect (Lee et al., 2020).Interestingly, the frontline employee that engages in customer-focused perspective-taking after experiencing customer incivility influences affective reactions to a negative event by mitigating anger and increasing empathy toward the customer (Lee, 2021).In other words, although frontline employees will face customer incivility, customer-focused perspective-taking can change or modify their affective reactions, as well as their attitudes and behaviours.

Perception
Several studies have attempted to include perception as an underlying mechanism either as a mediator or a moderator.Based on the analysis, the perceived threat has been used more often as an underlying mechanism in explaining the consequences of customer incivility.For example, Frey-Cordes et al (2020) modelled perceived ego threat as a mediator in explaining the relationship between uncivil customer behaviour and lower service levels.On the contrary, Mattar (2021) found that self-esteem threat mediated the relationship between customer mistreatment and anger as well as surface acting.
The analysis also reveals that most studies included a moderator in the customer incivility literature.For example, Cheng et al (2020); Qi et al (2020) found that hostile attribution bias moderates the relationship between customer incivility and negative affectivity and emotional dissonance.Similarly, Grandey et al (2012) found that climate of authenticity moderates the relationship between surface acting and job burnout.In these three studies, the moderators strengthened the relationship between customer incivility and its respective consequences.
Interestingly, the moderation-mediation effect was also found in the customer incivility literature.Cheng et al (2020) found that hostile attribution bias strengthened the mediating effect of negative affectivity on customer incivility and proactive customer service performance.Qi et al (2020) also found hostile attribution bias moderates the relationship between mistreatment by patients and nurses' turnover intention through emotional dissonance.
A trace of empirical evidence from the literature indicates that not all modelled study variables explain the underlying mechanism between customer incivility and emotional response.For example, perceived interactional justice (Frey-Cordes et al., 2020) was not a significant mediator in explaining the relationship between uncivil customer behaviour and lower service levels.Hostile attribution bias also was not a significant moderator in explaining the relationship between mistreatment by patients and work meaningfulness as well as nurses' job satisfaction (Qi et al., 2020).

Attributes
Customer incivility is found to be a major cause of stress affecting emotional response that was generated from interactions between service workers and customers (Dormann & Zapf, 2004) depending on the personal attributes such as individual demographics characteristics (Kim & Lee, 2020).Another attribute from the analysis is the locus of causality which reflects the extent to which people believe an incident was caused by them (internal) or by someone else (external) (Turban et al., 2007).However, according to Lee et al (2020), the effect of customer perspective-taking on customer compensation and deep acting via the mediating effect of negative affect is unaffected by the service failure locus of causality, implying that the mediation has no effect regardless of whether the hotel or the customer is the source of the service failure.

Motivation
Customer incivility may create an employee's intention to cause harm to other customers; thus increases employees' revenge motivation (Cheng et al. 2020), and mediates the effect of customer incivility on service sabotage.However, their study discovered that emotion regulation moderates the direct effect of customer incivility on revenge motivation as well as the indirect influence of revenge motivation on service sabotage.Customer incivility had a lower influence on revenge motivation, and cognitive reappraisal worked as a buffer for its indirect effect on service sabotage through revenge motivation.

Personality
Remarkably, personality such as agreeableness may lead to a positive reaction of frontline employees that can reduce the negative effects of customer incivility and enhance customer service (Medler-Liraz, 2020).Agreeableness is found to be moderating the perceived experience of customer incivility through customer orientation, where service employees who are high in agreeableness and core self-evaluations are more customer-oriented and are found to have fewer customer incivility experiences.Another individual trait, moral identity, is a powerful intervention factor in the connection between a person's moral assessment and behaviour (Liu et al., 2020).Individuals with strong moral identity qualities create less aggression when faced with customer mistreatment (Damon & Hart, 1992).When a person has a strong sense of moral identity, it might operate as a self-control mechanism that encourages moral behaviour (Hart et al., 1998).

Cognitive Reappraisal
Cognitive reappraisal is an antecedent-focused strategy (e.g., shifting one's perspective on a stressful situation) that has been shown to reduce the negative impact of customer incivility (Cheng et al., 2020).Rumination (i.e., repetitive thinking about an upsetting situation), in addition to cognitive appraisal, was found to aggravate the effect of mistreatment on service sabotage (Goussinsky et al., 2020).Despite the fact that rumination is generally used to obtain insight into the causes of problems, there is evidence that it actually serves to perpetuate or even intensify the unpleasant emotional reaction generated by negative events (Wang et al., 2013).

Transformational Leadership
Transformational leadership has an abundance of positive financial and attitudinal outcomes (e.g., Barling et al., 1996;Judge & Piccolo, 2004).It is defined in terms of four major components: individualized consideration (supporting and developing employees), idealized influence (also called charisma; enacting behaviours that are "ideal" to organizational functioning as a role model), intellectual stimulation (encouraging followers to think about problems in new ways), and inspirational motivation (developing and communicating an organizational vision, e.g., (Bass, 1998).Previous research proposed that transformational leadership influences both the primary and secondary appraisal processes of customer incivility by (1) fostering employees' ability to perceive customer incivility as a challenge with potential benefits for them within the organization, and (2) assuring employees that they have the resources (or indeed providing resources) to cope with this challenge, by encouraging emotion-focused and problem-focused coping (Arnold & Walsh, 2015).The relationship between perceptions of customer incivility and employee psychological wellbeing was moderated by transformational leadership.Transformational leadership appears to buffer the negative effects of incivility on psychological well-being, particularly when incivility is high.

Supervisor and Organizational Support
Supervisor support is the degree to which employees form impressions that their supervisors care about their well-being, value their contributions, and are generally supportive (Dawley et al., 2007).The research examined whether supervisor support moderates the relationship between customer injustice and employee display rule deviance through a reduction in employee anger.The results indicated that supervisor support did not have a significant moderating effect in the relationship between customer injustice and anger (Richard et al., 2016) In other words, the indirect effect of customer injustice on display rule deviance through anger was not found to be conditional on supervisor support.
Organizational support as defined by Rhoades and Eisenberger ( 2002) is "assurance that aid will be available from an organization to deal with stressful situations and when it is needed to carry out one's job effectively".Research revealed some significant moderating effects of organizational support on the relationships between workplace incivility, emotional exhaustion, and perceived service performance.The effect of customer incivility on frontline service employees' emotional exhaustion, as well as the influence of employee emotional exhaustion on perceived employee service performance, were moderated according to various levels of employee perceptions about restaurant organizational support (Cho et al. 2016) This implies when restaurant frontline service employees perceive a high level of organizational support, the effect of customer incivility on their emotional exhaustion is significantly reduced.

Job Control
Job control refers to employees' discretion or autonomy over decisions regarding task conduct, work methods, timing, and scheduling (Hackman & Oldham, 1976).The primary control concept is often reflected in autonomy such as job control in one's work environment.Thus, job control moderates the positive link between customer mistreatment and increased negative affect (Park & Kim 2018).This day-level link is weaker for employees with high job control than those with low job control.The findings show that job control is identified to reduce the within-person process of customer mistreatment affecting recovery outcomes.In other words, job control attenuates the day-level effect of customer mistreatment on negative affect.

Organizational Climate
Another contextual, yet extremely important, factor that may help slow the negative exchange spiral, is securing organizational support for service (Groth & Grandey, 2012).This might take the form of a "climate for service," which is a shared perception of the importance of rendering outstanding customer service while stressing the employee's value, boosting his/her engagement, and fostering his/her job satisfaction (Mattar, 2021).Grandey et al. (2012) highlighted the importance of a "climate of authenticity," where organizational members can openly express feelings with peers, in buffering health care providers from the strain of managing emotions in response to mistreatments enacted by patients.
Thus, customer mistreatment may feel unjust and seem to violate both interpersonal and moral standards of behaviour.These perceptions trigger anger as well as moral indignation, which can lead to emotional labour as well as to customer-directed aggression.However, providing an appropriate organizational climate may help to prevent an employee accelerates negative exchange spirals (Mattar, 2021).

Discussion
The objective of this systematic review is to identify the underlying mechanism that explains the why and how of the relationship between customer incivility and employee response.Frontline employees who interact with the customers are more likely to experience customer incivility when customers are not satisfied with the services rendered.Following the uncivil encounters, frontline employees will respond differently to the situation depending on the level of incivility severity.Regardless of the level of severity, all uncivil encounters will trigger frontline employees' responses.Some examples include emotional labour (e.g., Szczygiel & Baziriska, 2021;Zhan et al., 2021), emotional exhaustion (e.g., Alolaa et al., 2019;Yang et al., 2020;Yoon, 2020;Yue et al., 2020), emotional intelligence (e.g., Szczygiel & Baziriska, 2021), revenge motivation and service sabotage (Cheng et al., 2019); lower service levels to uncivil customers (Frey et al., 2019); employee revenge (Huang et al., 2018); rumination (Boukisa et al., 2020); and turnover intentions (Alolaa et al., 2019;Melhem et al., 2019).These responses are important to be managed so that no further severe consequences follow, which could harm the employees, service providers and customers.Therefore, understanding the underlying mechanism in mitigating or strengthening the response of employees who faced customer incivility is imperative, as demonstrated by the rise of the number of research on the topic in recent years.
Through our thematic analysis of the articles during the data extraction stage, we identified 44 variables which constituted the underlying mechanisms between customer incivility and the emotional and behavioural response of the frontline employees.We further reviewed these variables and categorized them into 11 sub-themes, which were then further categorized into two main themes, personal factors, and situational factors.

Personal Factor
The literature frequently addresses the negative chain relationships of customer incivility.Nevertheless, recent scholars open the way for new research to be conducted to measure customer incivility from positive chain relationships with the support of moderators and mediators.Based on the most significant trend in this study's systematic literature review, we identified several emergent themes that are categorized as personal factors, namely affect, perception, ability, attributes, motivation, personality, and cognitive reappraisal.However, not all underlying mechanisms will lead to the positive chain relationships without the negative impact at the first stage.
The link between customer incivility and emotional response is sometimes influenced by personal factors.Researchers have discovered that including such items is crucial in minimizing or amplifying emotional responses.Personal factors, for example, have been empirically proved to operate as intervening variables between the causes and consequences of employee psychological wellbeing (Fordjour et al., 2019;Quick et al., 2013).Every individual is unique, as human behaviour is the most intricate part.Personal factors, on the other hand, influence individual behaviour and can be divided into physical (e.g., age, gender, religion, marital status, and so on) and learnt characteristics (e.g., personality, perception, values, and ability).Individual differences in personal factors put them at a lower or higher risk of unfavourable outcomes.

Situational Factors
Situational factors refer to external or environmental conditions that do not accrue from within an individual (Kandala et al., 2011).Based on the analysis, situational factors can be further categorized into people-oriented and non-people-oriented.With regard to the people-oriented factors, several underlying mechanisms of emotional labour related to customer incivility were indicated in previous studies as moderators, among them transformational leadership (Arnold & Walsh, 2015) and supervisor and organizational support (Richard et al., 2016;Cho et al., 2016).
Specifically, in Arnold and Walsh (2015), transformational leadership was found to moderate the relationship between customer incivility and employee well-being.Similarly, supervisor empathy buffers the relationship between customer injustice and employee anger (Richard, 2016).In Cho et al (2016), some significant moderating effects of perceived organizational support (POS) on the relationships between workplace incivility, emotional exhaustion and perceived service performance were revealed.In these three studies, the moderators strengthened the relationship between customer incivility and its respective consequences.
Meanwhile, with respect to non-people-oriented, several underlying mechanisms in previous studies like job control (Park & Kim, 2018) and organizational climate (Mattar, 2021) have been included as mediators and moderators.For example, in Park and Kim (2018), job control attenuates the day-level effect of customer mistreatment on negative affect.On the contrary, in Mattar (2011), the absence of an organizational climate supporting service employees accelerates negative exchange spirals.

Conclusion and Future Research Direction
Research related to customer incivility and its consequences on frontline employees has gained traction over the years.In recent years, more researchers began to study the moderating and mediating effect of employees' emotional and behavioural responses resulting from customer incivility.This review probes deeper into the specific underlying mechanisms of customer incivility and employees' responses to it.Specifically, this study identifies the elements that mitigate or escalate such responses, either positively or negatively.Based on the systematic reviews performed from articles published between 2010 and 2021, authors have identified 44 variables which constituted the underlying mechanisms and categorized them into 11 sub-themes, which then further categorized into two main themes, personal factors and situational factors.
Interestingly, personal factors were found to be the most used underlying mechanisms in previous studies as compared to situational factors.This finding implies that organizations need to provide and enhance existing training on effective coping strategies for the employees.It includes preparing and delivering training content that aims at recognising and regulating employees' personality, abilities, affective responses, perception, motivation, and cognitive reappraisal when facing uncivil customers.These interventions, which are executed at the organisational level, could benefit frontline employees since they may influence to a certain degree of the work processes, relationship with customer and the organization image.
Although situational factors received less attention than personal factors, its importance in influencing frontline employees' responses when encountering uncivil customers should be acknowledged too.Thus, organisations must provide the necessary support to the frontline employees, which includes leadership and supervisor support as well as organisational support, in incidences involving customer incivility.Such support when coupled with a positive service climate and job control could mitigate the negative responses and hinder the incivility spiral.
In this systematic literature review, our focus was on the relationship between customer incivility and the frontline employees' emotional and behavioural responses.
Although the emergent themes emphasise on the strategic importance of managing these responses, there are other possible avenues that future researchers could explore further.Specifically, we recommend future studies focus on the relationship between other types of incivility (e.g., workplace incivility or cyber incivility) and employees' emotional and behavioural responses.Besides, more qualitative studies are needed as it offers in-depth analysis and detailed explanations on employee adaptation methods to mitigate or escalate the employee's response.

Figure 1 :
Figure 1: Flow diagram of the SLR process Note: Adapted from Shaffril (2021)

Figure 4 :
Figure 4: Years and Number of Publications

Table 2
Inclusion and exclusion criteria