Without considering the law or anything, if it was my 12" PB and this other person was trying to help me find it (whether or not I asked him to help isn't part of the issue), and he finds it but hits the bottom of the next shelf above and then accidentally drops it a very short height, I wouldn't charge him or expect him to pay. Scratched or not, he was just trying to help, after all.
If I misunderstood the original post and this guy wasn't trying to help you at all, and just picked it up when you weren't there because he saw it and was curious, then yeah, I think he's responsible, but I wouldn't really charge him to get the scratches repaired. Getting something like a PB fixed would probably cost way too much to be justified.