Involving in business both with random guys and those we know has different scenarios. Why because there are some certain business we will loved to do with those closer to us and vice versa same goes for other people we do not know and we will still make business with them.
In aspect of buying crypto currency or digital currency is better to stay away from unknown individuals and not to do that business with them, we rather take ourselves to the exchanges and get our deal done through p2p or any other means because making business with unknown users outside exchanges comes with a lot of risk so let avoid it.
The irony here is that the two parties in the OP’s story know each other, while when you make a trade on a P2P platform you only know what the platform chooses to share about the other party with you.
Personally, I would still buy those coins even if they are sold at a discount because I believe in Bitcoin’s fungibility and that it’s one of its main fundamentals. I also believe that tainting coins by exchanges is not right.
Howevet, I wouldn’t buy them if I knew they were stolen as I can’t/don’t want to encourage criminals.