I have sold items that I was almost certain were not \genuine - but in every case I describe the items in detail including the fact that I believe or know they are reproductions.
It someone insist on selling fakes, then contact Ebay. Some repros are worth more money than the originals.
You can't protect every buyer that wants to make a big profit on every buy. Nor should you, life is the best teacher.
Do your bst to warn unsuspecting people, let the others learn the hard way! I have bought any crap pieces ( which I represent as crap) nd we all sort of still keep on living.