Social custom and psychological theory both suggest that hospitality customers leave tips as an incentive/reward for good service. However, previous research has found only a weak relationship between tips and service in restaurant settings. To see if this finding generalizes to other service contexts, we had a hotel bellman randomly assign his customers to receive either "limited service" or "full service" and to record the tips those customers gave him. The bellman's average tip was $4.77 in the full service condition as compared to only $2.40 in the limited service condition. This finding suggests that tipping does serve as a strong incentive/reward for bellmen to deliver good service.
Lynn, M., & Gregor, R. (2001). Tipping and service: The case of hotel bellman [Electronic version]. Retrieved [insert date], from Cornell University, School of Hospitality Administration site: http://scholarship.sha.cornell.edu/articles/155