No, I would not. It just would not feel right and the guilt would eat me alive. I know there are people who do this kind of thing, but it's just not in line with my values. I was raised with a strict ethics code: if you are given too much change, you return it. If a store forgets to ring up one of your items, you let them know. If you find a stray item on the ground, you turn it into a lost & found or leave a note in order to try and locate the proper owner. In fact, something like this happened just yesterday. My best friend and I are on vacation in the Bahamas right now, and we were accidentally given someone else's room key which is linked with their credit card. We didn't realize there had been a mistake until we went to pay for our meal-- and they called us by this person's name. When we realized, we had the restaurant cancel the check, had them charge our card instead, and gave the card back to the hotel so no one else could use it.