I have seen this all the time in the Digital Good board. One guy creating several threads, locking them, and selling fake stuff on Rocketr. Of course he had negative trust on both websites, but people don't care...
And theymos doesn't care either, and that's most important. Scams aren't going to get moderated here unless he decides to do it, and what OP described is a subset of scam. Wouldn't be hard to make rules and enforce them--you just have to nuke topics and ban users. I don't want to hear excuses for the status quo. Other forums can do it just fine. You don't need an army of mods, just the will to act.