Drawing on the customer participation (CP) literature, this research proposes that CP variation is the degree to which employees perceive variability across customers with regard to customers sharing information, time, and effort and making suggestions to enhance the service delivery process and outcome. Drawing on the job demands–resources model, this research explicates the mediating process by which CP variation affects customer service performance and its boundary conditions. Study 1 uses data from a field study in the banking industry to show that CP variation negatively influences customer service performance through greater customer-related burnout. The authors show that this mediation process is moderated by contingencies that mitigate or exacerbate the indirect relationship. Study 2 further validates the CP variation construct by testing for discriminant validity against similar and related constructs, such as CP quality, in more diverse service industries (insurance, legal consulting, travel and tourism, health care, and physical fitness). Finally, an examination of the moderating role of CP quality provides a more nuanced picture of the intricacies between CP variation and CP quality. This article concludes with a discussion of the theoretical and practical implications for CP variation research.