Don't parents "bribe" their kids all the time? "If you eat your vegetables, you can have ice cream for dessert." "If you do your homework without complaining, you can play Wii." This system of good-behavior-equals-reward starts at a very young age.
When we offer to do something children want in return for helping us when they would rather be doing something else, this is not always a bribe. It can also be an expression of appreciation and an opportunity to teach the importance of reciprocity.