James Surowiecki says, Check Please:
It’s instructive to consider the sort of things that tippers actually respond to. In one study, a waitress received fifty per cent more in tips when she introduced herself by name than when she didn’t. In another, waiters sharply increased their tips by giving each member of a dining party a piece of candy and then, seemingly spontaneously, offering each person a second piece, too. Squatting by the table instead of standing, writing “Thank you” on the back of checks, and touching customers on their shoulders all measurably improved tips. And waitresses at an upscale restaurant who simply put flowers in their hair boosted their tips by seventeen per cent.