Buying favours, or bribery, is a practice that has been abhorred in most cultures for a long time. In the English-speaking world, it is certainly frowned upon. Yet many parents use bribery as a form of control for their children, or even their spouses. ‘If you don’t do your homework you won’t be going to the movies.’? ‘If you eat all your vegetables, you can have some ice cream.’? ‘Do as you are told...