<putting on tin foil hat, with apologies>
Any chance that the person who bought BTC from you, Dan, could have been the person who owned the wallet address where the BTC went to, with the hope some, if not all the $ were returned to him?
<off, again with apologies>
It's a legitimate concern, but in this case I'm as certain as I can be that it isn't the case.
The user "themad2403" over at hackforums.net has admitted to being the thief, and it has been determined with relative certainty that he is hispanic.
He has refused to return the bitcoins to the victim.
I've dealt with the guy who bought from me in the past, he isn't hispanic, and I'm certain that he doesn't have the skills to pull of a such a scam right in front of me on his own.
While a possibility could exist that he was working with someone else who was not there and was waiting for the bitcoins to be deposited so they could quickly sweep them out, he'd have had to be a pretty impressive actor and have worked out some pretty good timing.
Given how many scams we see on a daily basis, I think we all carry tin foil hats around with us. In this case, I don't think its warranted.