We have an arrangement with our kids. It goes something like this: if we're in a restaurant and the server gives us an unsolicited compliment on the kids' behaviour, they get dessert. Dessert is not necessarily gotten at the same restaurant, although it makes it easier to keep tally when it is: sometimes we really need to get somewhere on time, or the dessert selection isn't worthwhile, or something. But there is dessert in it for the kids whenever a server compliments their behaviour with no prompting.
This arrangement has served us well, but it has started to get expensive: the kids have started to rack up the compliments, and it's harder and harder to keep tabs on what I owe them.
Which, I suppose, is better than the opposite problem.