It seems to me that the appropriate action would have been to keep the other thread open until the issue was resolved. At this point, all there is are promises that a resolution will be reached, which, in the world of cyberspace, are meaningless until proven. As the seller admits himself, the complaint is merited.
Deleting that thread doesn't address the seller's credibility; it rather masks it. That couldn't have been the seller's intent, could it?