Yes, I think it's appropriate, and in the best interests of the community. If the seller had personal issues, perhaps his judgement was clouded, but that gives nobody the right to abandon ethics and fairness. He reneged on a done deal, with absolutely no hint that the buyer was going to default. That's about as bad as it gets for a seller's rep.
Seriously, if Comicsupply or some other past notorious character on here had done this, they wouldn't only be on the probation list and hall of shame, but the calls for their banning would be deafening.