newboyintown
·The advice here is all excellent. In particular, the private watch sales forum is, imho, simply the _best_ avenue towards acquiring reputable, high-quality vintage Omegas at extremely fair (perhaps even over-generous) prices. Many of the watches sold there would command significantly higher prices on ebay, chronowatch, etc., but members want to keep them within the community, so they go this route instead.
That having been said, I don't see any Cosmics for sale right now. But there is a very nice pre-cosmic SM in a forum I don't ordinarily recommend, Gumtree. I considered this one myself, however, and corresponded with the seller, and everything looks on the level (though I would try and get them to come down £50-75 on the price). It is not, as advertised, a 565, but rather a 752, I am all but certain (though haven't seen the inside). https://www.gumtree.com/p/mens-watches/omega-sea-master-vintage-watch-£675/1361003242
I’ve seen one on here on the private sales,
FS Omega Seamaster De Ville - Reference 165.020
which I like the look of.