Unfortunately, the Amazon support people said I'll simply have to e-mail my buyer about this and ask them if it's a return or not. I haven't e-mailed them yet because I'm afraid I'll be very accusing or rude which won't help my case at all.Thank you though for all your ideas and opinions.
@James - I can give negative buyer feedback, but most sellers don't look at that. I suppose it's better than nothing. It's also going to suck because they are going to probably ruin my perfect 5-star feedback if I don't refund them right. As for law, I double-checked USPS policies and while I am right, I have no proof of the repackaging since I had already opened it up (stupid on my part). Best I can prove is they held onto the book for 9 days before refusing, unless some mail person ACTUALLY remembers a certain package, heh.
Oh and funny enough, I live one town away from the buyer, I could easily drive to them. BUT on google maps, it showed they live in an apartment, so egging their house or something would hardly be productive. When I can find the right words to e-mail the buyer with, I'll give another update about that here.