I think this might be against the law. I'm not sure that you're able to detain peoples property unless they pay you even if you found it. Most people, including me, would be thankful that someone found the disc and would be happy to pay the finders fee, but if someone really wanted to make a big deal about it you would probably have to give it back for free especially if they can prove its theirs like if their name is on it.
Oh, part of our deal is that if we have their disc, no matter how we got it, they get it back. Absolutely. I noted that above. We got a bunch of discs in a few weeks ago, used, from one person. And we called about 20 people whose names or other ID info we could find on them. Only one wanted it back, and we're holding it for them. The others all said they had given away or sold the disc to someone else and could care less. But if they showed up in the store and said it was theirs, then it's theirs. I think that's the only fair way to handle used discs.
I think this might be technically true however I don't see police and courts being willing to get involved over a $2 finders fee. And if someone is really willing to be that much of a douche make them jump through all the hoops to get the law involved and then say "ok here's your disc". Then everytime someone shows up with one of his discs tell them what a douche he is and you don't want the disc.