Was there any value to the “post in the thread before purchase to help reduce scammers?“
You were supposed to post in the thread in order to prove that you weren't banned from the subreddit. I know the ban list got fairly long over on watchexchange, so I assume it was preventing at least some scams. I think the same thing would work here. But IMO the most trustworthy buying and selling subs were the ones that had some kind of "verified purchases" bot, where the buyer and seller would tell the bot about the transaction and then it would add to your transaction count. That would be a great thing to have.