Interestingly enough, there are drastic differences written in law regarding this. In some countries, you are in fact allowed to keep purchased stolen goods, if they were bought in good faith. While in other countries, you as the buyer can be in serious trouble, even if you couldn't know if it was stolen and at least need to prove that you were misled and did everything you could to prove ownership.

I guess you were arguing morally, just pointing out this isn't legally true everywhere.