biggest exit scam I remember Toonvendor. He regularly sold multi thousand dollar wow accounts and in the end scammed many people. Like this was THE GUY to get accounts from. Even got a friend of mine who cashed out toonvendors paypal balance to cash and then recalled the funds. That kid never really recovered from the loss. Lost his paypal and collections came after him. Toonvendor was in the news at the time for scamming minimum 20k usd from various people.
I remember a young canadian kid here who scammed like 4000 dollars on his way out because he was a minor and no one could find out his information due to privacy laws. He was a jerk about it too, like all proud of himself.
As far as moderators scamming here, we have had a good bunch of people, only a few bad apples. One sold of a bunch of wow name changes and ran with money. Maybe 2k. Another was into fake id's and stealing wow accounts and reselling.