The fact that you're asking probably means that you already know the answer. There's enough trouble out there without adding one more kiddie hack to the list.

The responsible thing to do would be to alert the store manager that they have a problem. Most electronics retail people like to fancy themselves computer experts, when in reality most of them don't have a clue. Try to explain about password security in a way that will help them, but not sound condescending or make them feel dumb.