A few years ago I sold a gun on there and I had about twenty bidders. I looked at the ratings for each bidder and noticed one had a bad record of not paying. He was one of the bidders that kept putting bids in on what I was selling. I contacted GB and asked then to remove his bids and block him as a bidder. They were happy to comply. I have always had good luck buying and selling there. Contact them about your issue!
Require Postal Money Orders. If fraud occurs the Postal Inspector will get involved on your behalf (at least that is what they say they will do).
Strive to live up to the opinion that your dog has of you.