In general, I don't like the idea of bribing for good behavior. I think it should be communicated to the child that good behavior is expected, i.e., the norm. On the other hand, rewarding for good behavior now and then is fine. (The difference between a bribe and a reward is when you tell the child about it ... a bribe is "If you do this, I'll give you something good." A reward is "Hey, you were exceptionally polite when Aunt Gertrude came over. How about we go out in the backyard and play catch?").