Aren't morals fascinating? If you had found an actual item in a box worth $1,000 you wouldn't think twice about selling it and profiting. But since it was actual cash, you feel an obligation to return it. What's the difference? You didn't steal it ... you purchased something that ended up being worth much more than you originally anticipated.
Not saying that you should keep it (or return it) ... but just a fascinating scenario!
Gotta agree with Fushek. This is just like if you buy a home( or a home off auction, site unseen) or if you purchase a Storage Locker . You get the good along with the bad. Plenty of costly surprises or maybe you find some hidden treasures. You bought the Home/Storage unit and all it's contents. I wonder how many return items they buy at storage units since just about all units are confiscated.