I learned my lesson, NEVER buy from someone who is not an expert and cant confirm the condition of the camera beyond it's physical appearance.
I strongly suspect that some ebay auctions that state "Super clean, mint, sold as-is with no returns because I can't test it / don't have film /don't have a darkroom / don't know how it works" are people who know damn well it's busted. Not all, maybe just a few, but it's a reasonable thing to claim in the digital age, and a way for people to get higher crap-shoot dollars out of broken gear.
If a seller can't state specifically what's wrong or says they can't test it, I check their feedback and other auctions - often it's clear they're a photo dealer. I message to see how quickly they respond, ask them to check specific things. If it's an absolute steal (almost bought a pro-s body with just the focus screen for $45, probably parts in there worth having) I might take a chance. If someone is happy to crank a knob, describe a shutter click, shine a flashlight in a lens and reply back, I figure they're at least trying to give me the best idea of the gear possible. Many sellers really go the extra mile when asked. Many never answer
but heck, a Minolta rangefinder, untested, for ten bucks - I bought one and got it running just fine. Sweet little carry-around camera.
I've gotten some very fair deals on eBay and a few fantastic ones and it's a great resource
when used with caution.