Restaurant tipping in a field experiment: How do customers tip when they receive too much change?

Tipping behavior is analyzed in a field experiment where restaurant customers received excessive change, either 10 or 40 Shekels (about $3 versus $12). One third of the tables reported the extra change to the server and returned it. Tips were higher with the higher level of extra change. Returning the extra change was negatively correlated with tips. The interaction between the level of extra change and whether it was returned had no effect. Possible explanations that tips are higher when the excessive change is not returned due to a positive income effect or perceiving paying a tip out of excessive change as less costly because it is a forgone gain and not a loss, are not supported by the data. Subjects may have exhibited moral licensing and moral cleansing effects. These effects, however, were possibly mitigated by a self-selection effect going in the opposite direction: those who are more generous or altruistic by their nature are more likely to return the extra change and also more likely to tip generously. Receiving the larger amount of extra change may result in feelings of good mood, perceived luckiness, or individuation and unconscious fear of being observed, which increase tips. Interestingly, these feelings seem to remain even if the extra change was returned.