The problem is your logic. Stolen is stolen, if 
you knew it or not doesn't play a factor. You 
either return the item, whatever it may be, or 
you pay the value of it. 

When my car was stolen last year, the person who 
bought it from the theif thought the same... He 
didn't know it was stolen, spent a lot of money 
on it, he likes the car and felt it was my fault 
for not have a better car alarm. He didn't see 
anything wrong with buying a car with no title 
either since as he put it "who uses those papers 
anyway?"

I'm sure cels are similar. If they're stolen and 
the original owner finds them, you have to fork 
them other.