As long as the OP is willing to use a trusted third party escrow chosen by the buyer, what is the risk? I agree that the OP seems shady, but he has proven ownership of the BTC he is trying to sell, and assuming he agrees to use escrow, why shouldn't people do business with him? Refusing to buy his coins won't make him pay back anyone if this is in fact Marc. As long as the buyer exercises proper caution, they are not at risk in my opinion.