Having just been in a training thing about business ethics, one example situation they suggested was getting the bill at the end of a meal but they had forgotten to add on the drinks - would you say anything?
Everyone in the room laughed and said 'who would tell them', but I have to confess this exact situation happened to me a few years ago, and I did tell them (H wasn't very impressed that I did though!). Am I in the minority? Would you tell them they'd forgotten to add on the wine? If it makes a difference, in my case the wine was about £15, and the meal (Chinese) about £20...