the smug sense of superiority that I bought with the Mac has been wiped out

Thank the gods. Platform chauvinism is boring. Trying to achieve and maintain self-worth by buying a specific brand is sort of silly.

In fact, eBay does work with a third party mediation company, SquareTrade to help buyers and sellers resolve conflicts. It's one of the services listed on eBay's services page.

Granted, like in most mediations this does not guarantee a favourable outcome. But if you feel you have been defrauded of something, most credit card companies protect the buyer anyway.