Again compairing to stamps... There are some very talented 'stamp restorers'. If done as preservation, museum display etc, can be a good thing. If they find there way on the market pretending to be originals, its a whole different thing. Most notorious, a guy by the name of Jean de Sperati fooled many experts. Story is he got ripped off buying from a reputable dealer who thought his stuff was genuine. Another dealer said it wasn't... So Jean set out to prove he could fool the experts. He never actually tried to make money off them himself. Made many fakes that are now considered collectible in their own right.