n00b vintage hunting

Hello everyone I'm Sam and I'm new here.
I have owned new production Seiko, Citizen, various Swatch Brand, various oddball mechanicals, and vintage Seiko that I know pretty well, but right now I have my heart set on a vintage Omega in an affordable price range, ideally $500-$600 (before shipping/authenticity guarantee/taxes/etc).
I actually already bought one on eBay, and it did not pass the "authenticity guarantee"... which is good, because I don't have to pay for a bum watch, but it sure is a wild world of watches out there.
Original parts are more important than perfect cosmetics. In fact I don't really want squeaky clean. I want authentic, cool, and functional.
It seems as though there are a lot of sellers in Japan and I guess its basically just an $80 risk if you want to buy a watch (to go through eBay's authentication) which is fair and helpful (they were thorough).

Anyway, if anyone has tips to send my way, I'd appreciate it. Looking for pre-1970, something men's, not huge (which doesn't seem to be a problem with vintage), and of course something functional.

The stickied threads have been super helpful but if anyone has tips or just wants to say hi, let me know!
Sam

It was actually not an issue of counterfeit parts, but rather that it was advertised as winding properly and it did not wind properly.

Exactly !! I had to educate the authenticator after they passed a non original bezel. It's hit or miss.