I used to go to a lot of small local live auctions. The mirrors and the chandeliers like to bid. You get to know the dealers and how they work together to sometimes divvy up the lots. When you become a regular, then in a way you become part of the system.
The words 'Caveat Emptor' have a lot of meaning. It is pretty much a get out of jail free card. Still one can accumulate a lot of 'stuff' that way.
A lot of my collection from the 1990s came from NAWCC silent auctions. Where you wrote your bid on a slip of paper, then someone would blow a whistle, and who ever had the highest bid won. Omega was not popular at the time with the dealers who had been burned with a flood of fakes. Other times it was boxes from the DWC that had been cherry picked over. (DWC dead watchmaker corporation aka watchmaker estate lots.) The parts on eBay seem to be much the same thing.
I'd say about 90 percent of the stuff sold at the major and minor auction houses is legit. There is a great film called 'Red Violin' which was based on the sale of an expensive violin. How much is true is anyone's guess, but it certainty seems plausible.
There is also the case where Swatch/Omega got caught with the hand in the cookie jar. So no more archive extracts, which were being used to legitimize things, even though there was a disclaimer. So there are industry watch dogs, with websites and publications, who will call out the more egregious stuff.
In the library one can find a section of books about art fraud. Which is really fascinating. The name Hans van Meegeren comes up a lot. Then there is also Ken Perenyi.
I do have an ebay addiction, so I still tend to look for that 'hit' bidding on the lower end of the spectrum for what is basically garbage. Rusted out rat watches. But it entertains me.
Lately I have been playing about with Claude AI. And managed to burn half a weeks worth of usage tokens in 24 hours. So no new eBay watches this month. Google AI is pervasive now in search. So I just downloaded that desktop app as they claim more usage, but still limited on the free or introductory plans.