Beware, buying vintage watches on eBay is 'hard mode' even for longtime collectors. The number of 'Frankenstein' Omegas and other older pieces likely outnumbers the legit ones, and the degree to which -- and skill level with which -- things have been refinished or repaired is often very difficult to ascertain.

The other thing to beware is that the fake market ("replicas") is now unbelievably good - and also include vintage pieces. So scammers could buy very good fakes, artificially age them, and charge a fortune.

The only thing that works is to 'buy the seller' meaning: only buy from reputable sellers/dealers.

Chrono24 and (carefully) using r/WatchExchange are your best bets, but even there - diligence the sellers very well.