@Jan
Hello,
I have no problem with face-to-face clients. I would give out a double receipt : one copy for her, one for yourself. To make it look professional "oh, i do this all the time", then sign them both YOURSELF FIRST, and then ask her to sign both copies. Say it is "for the record" because you like to keep track of everything ordered and sold and DON'T give excuses! This is a business transaction, after all! Quite simple, really, and the bad apples wouldn't have a chance to protest. If they did, you know that it may be better not to deal with them.
As for listing, make it a "custom listing" if you are selling it through etsy, that way you only pay 0.20 cents (not 30 x 0.20cents)!