In many hospitality workplaces, customer deviant behaviour is no longer an occasional frustration but a routine part of frontline employees' day, steadily draining their energy, dignity and desire to deliver great service. Yet in sub-Saharan Africa, especially in Ghana, there is still limited evidence showing how this behaviour undermines employees' motivation and what can realistically be done inside organisations to buffer its impact. This study explored how mistreatment from customers affects the service motivation of frontline employees in Ghanaian hotels and examines whether supportive supervisors can act as a protective buffer. Using a quantitative cross-sectional survey of 508 frontline staff in licensed hotels in the Kumasi Metropolis, the study applies Partial Least Squares Structural Equation Modelling (PLS-SEM) to test these relationships. The findings reveal that when customers display deviant behaviour, employees feel less motivated to offer high-level service. On the other hand, strong supervisor emotional support uplifts service motivation and partially mediates the harm caused by deviant customers. These results show that everyday supervisory support (listening, empathizing, and standing up for staff) can make a tangible difference to how motivated employees feel after difficult customer encounters. The study therefore offers practical guidance for hotel managers who want to safeguard employees and sustain high service standards in demanding customer environments.