Purpose - Many service employees rely on non-contractual voluntary customer tips as a major source of their income. The purpose of this paper is to empirically test the relationship between the service employee s cognitive evaluation of the tip (expectations-disconfirmation tip gap), affective state (AS) and displayed emotions (DE) toward customers in the workplace. Design/methodology/approach - An experimental, between-subjects, scenario-based research design was conducted on 107 waiters in the US restaurant industry. A simple mediation model was first tested, before testing a more complex moderated mediation model that was developed to investigate if employees self-control (SC) moderates the relationship between the employees tip gap, AS, and DE. Findings - An employee s negative disconfirmation tip gap negatively influences the employee s AS, which in turn results in negative DE toward customers in the workplace. However, an employee s positive tip gap does not positively influence the employee s AS, relative to the control. In addition, employees SC does not moderate the relationship, which suggests that when employees experience negative tip disconfirmation they may openly violate the service provider s display rules and service scripts, and display negative emotions toward customers in the workplace. Research limitations/implications - The scenario-based research design was limited to self-reported perceived levels of SC and DE. The scenario was also limited to one country and one tipping context (i.e. restaurants). Future studies could compliment these findings by conducting both qualitative studies, and survey research that relies on actual tipping data or re-enactments of actual service encounters. Practical implications - Service managers not only need to manage display rules and service scripts to influence employee DE, but also need to manage employee tip expectations, especially when employees expect to receive tips that are greater than actual tips (i.e. negative disconfirmation). Communicating and educating employees on customer tipping and what tips to expect should be central to managing employees who rely on customer tips. Originality/value - Tipping has received very little attention in the services management literature. This study broadens the focus of tipping research in the literature by presenting a more complex expectations-disconfirmation tip gap model.