This post reminds me of the one a few months ago about buying kitchen cabinets from a soon-to-be-foreclosed house.
Buying goods that you know are are stolen makes you an accessory to the crime. And a slimeball, IMO.
It's wrong, you know it's wrong, and no amount of rationalizing will ever make it right.
Decide what kind of person you want to be, and live with your decision.
Perhaps my friend is a slimeball? Perhaps he should have explained the value of the stone... but he doesn't KNOW the ring was stolen and I CERTAINLY don't know it!
I guess I will leave this conversation now