Throwing a little extra change to the waiter, delivery boy, taxi driver, grocery store bagger, moving man or masseuse is supposed to be a sign of generosity. A 2012 study out of Harvard University, however, shows that countries with higher levels of tipping also tend to have more political corruption. The study's authors say that the correlation may be explained by a simple principle of free market economics: There's no such thing as a free lunch. Heavy tippers, just like people who use bribes to open political and business doors, expect the gratuities will get them something in the future [source: Torafson, et al].
The study authors said the link is strongest for those whose tipping has a "prospective orientation (to obtain advantageous service in the future)" rather than a "retrospective orientation (to reward advantageous service in the past)."