Anybody Else Have This Problem?

I wanted to know if anyone else has had this particular problem. I'm sure someone has but I'd like to know opinions on dealing with it. I'd sold one of my sketches and the person who bought it asked if I had any more from the series I was willing to part with. Mind you, this was at a time when I was particularly broke and was willing to sell my little brother to get some cash. So, idiot me said yes and sent her pictures and such of various sketches I was willing to let go. She bought five more. Okay, no trouble so far. I started to get weird inklings, which I should have heeded, when I said I could only take money orders and she kept bugging me about my paypal address. Anyway, she sent me the money and I sent her the sketches. I try to make sure that any sketches or cels I send out are very securely packaged, usually inside enevlope, then cardboard on either side of that and bubble wrap package or mailing box. So, a week or so later she emails me and says that some of the sketches got torn due to the inside envelope seal. I never seal the inside envelope unless the sketches are small enough to fit completely inside without sticking out. Again, idiot me ignored my gut instinct that said something was wrong with this picture. I told her that I'd refund her money for the torn sketches if she'd send them back to me. She said she wanted to keep the ones that weren't torn and we worked out how much of a refund I was to send her. I sent her the refund and never got the supposedly torn sketches. Tried emailing several times and got nothing back. I know the vast majority of this is my own fault but I'd like to know if anyone else has dealt with something similar and what was don concerning it? Thanks.