You might want to consider the following. Each card, of course, is supposed to be used only for the restaurants in the book from which it came. Each card has a number on it that identifies the book from which it came.

Restaurants often file a card, similar to the old fashioned credit card slips, with Entertainment by running your card through their machine. I assume that Entertainment can tell if the card was used for a restaurant from a different city than what was intended. I'm not sure what they would do with that information, but it is something to consider.