[genchan]

I would keep the money. If they gave me a the wrong change in their favor, would they give me the correct amount? Not unless I check and demand it back...and I have to do it right at that moment. If I go to my car and find out they gave me the wrong amount in their favor and go back in to tell them, would they give me the correct amount? No. They would say there is no way to know and I should have made sure sooner. If they would treat me that way, then they are also responsible to check and make sure everything is correct when they give me the change. If it is wrong, then it is their mistake and I would keep it the same way they would do it if I didn't check.