Sheer stupidity, as you say. I would never, ever buy an instrument through eBay that I couldn't play in advance and try out. And there would certainly have to be a returns policy if a fault was found after the purchase.

The word "vintage" must be one of the most overused and misleading terms on eBay. For many things "vintage" just means "tatty old crap of no value, but it's old"!