Bad negative feedback?

This guy gave gave me negative feedback on a game saying it was unplayable and had a bunch of scratches on it. The last game I sent to this guy he gave negative feedback before he played it. He just assumed it didn't work by looking at it. The disc I just sent him had some scratches on it, but no more than just from normal use. None of the scratches are deep, just small cosmetic scratches on the surface. How can I keep him from screwing me over on a working game ?