A waiter stealing credit card numbers has a good chance of being caught eventually. I assume the credit card companies do some basic data mining on their stolen card database, and if card numbers start getting stolen shortly after dining at a particular establishment then they'll track this down.

I googled "waiter stealing credit card numbers" and here's an example from today's news of some folks who got caught:

http://www.wjla.com/news/stories/0510/739156.html

On the other hand if you have a radio scanner and are picking up numbers going over the air from tow truck companies there's no traceable link between you and anything in the database.