I would imagine it's very difficult to moderate every sales post, but I am sure everyone here does their utmost. I remember in each advert there used to be a panel where previous buyers could show as references for a given seller. This seem to have been lost in the latest website update. I always thought that was a good idea.
As this has becoming more prevalent, for the last few watches I have been looking at, I ask for references and try and marry those up in some way with known people in the website (checking post strings etc.) but it's not infallible. there was a watch I have wanted for some time shown a little while ago, but I left it in the end as the seller was always whatsapp'ing the possible reference before I got any detail back, so a bit tricky to know if some subterfuge was going on. Being in the UK it's even more difficult as most watches listed here are in the USA or Asia so a bit awkward for any redress if things go wrong
Maybe a sub folder in the collectors market for advice and horror stories so anyone can look at what has happened in the past and take note (not that this helps those already robbed of their cash)
The dark belly of the internet unfortunately, very sad indeed
regards
Tim