I do maybe think that your feedback is a bit OTT on this occasion Vod. While I usually agree with the trusts that you leave, leaving one because a user might do something is rather stupid. If you're doing that, you may as well negative tag every member here since they might scam someone in the future.
I think that a neutral would be better, if not removing the feedback all together.
That's not quite a fair comparison... not everyone makes a throw away account to sell something gullible newbies want to buy.

Almost everyone who wishes to sell their account will use an alt account to do so. A decent amount of these people do not have an alt account so they create a throwaway account to sell their account.
I don't see any reason why the OP should have negative trust, although I would still advise anyone considering to deal with him to use escrow to protect all parties. From the looks of it, all you have accomplished is make you look like a fool.