I bought three tee shirts and a vest the other day from Hot Topic. A few hours later I ran back to exchange the tees for smaller sizes (vest was unchanged). The cashier asked if I wanted the original receipt back and, like a dummy, I said no.
Later on I started worrying about whether the vest would need to be returned... and the fact I'd have to take a store credit since I no longer had the original receipt. I went to the store, explained my situation, and the two girls were very helpful. They went into the back room and found my original receipt, and also printed out a duplicate receipt for me. They were extremely polite, didn't get annoyed at having to do a few minutes of looking around, etc.
Figured I'd write something positive on their behalf.