If he is being a jerk about it maybe give him his money back and tell him to get lost. Then leave him bad feedback for being a jerk. I don’t see why he couldn’t wait a couple of days while you get your new camera.
As far as him leaving you bad feedback atPS. That is laughable. The member list of MPS reads like the whose who of frauds, cheats, and reprobates. It is the blighted crack den of panties. Everyone there is only there to rip each other off and bash each other. Amassing bad feedback there is like a rite of membership. If you are an honest seller you’ll never be accepted by the cretins who frequent the site.