That negative feedback ought to be removed. The system is intended to provide public details about a buyer and seller after a transaction has occured, not a potential buyer or seller for something that hasn't happened yet unless the violations are particularly egregious.
Gcoap is in the wrong for leaving negative feedback for the sole reason that he wasn't responded to promptly. How do you know his mother didn't die in a horrible car crash and he was 1000 km away attending her funeral? If you were so concerned about purchasing his product you ought to have sent him another message asking if he'd received the previous one, that at least would have demonstrated something of a commitment to making a purchase. However by the sounds of it no other efforts were made on YOUR behalf to establish further communications, you just jumped to a hasty conclusion and utilized a tool which, by most standards, you hadn't the right to use yet.
I hope a mod is able to clear Gonepostal's record of this asinine charge.