Any seller who is numpty enough to leave false pos feedback does themselves, and other sellers, a grave disservice.

Only according to a very, very few posters who just happen to be highly active on the buying/selling discussion boards, however overtime, whilst I am not such a prolific poster,  I have viewed numerous threads and posts from a far wider range of sellers on this topic who IMO would strongly disagree that they are doing a disservice to other sellers.