Not paying up after winning.
Hiding bids/retracting bids.
And a specific situation;
Someone had bid on my auction, was locked in a bid war, noted me, and claimed the other person was cheating and wanted to retract their bids. The other person was not 'cheating' or breaking any of my rules what so ever. Said person (who noted me) also tried to dictate my rules (no multi bidding, which was allowed, and the person did them self) and tell the same bidder what to do.
Should I disqualify him? But, this would also make the bid war useless, and I'd hate to rehost it because one slot had to be reset. What should I do? I don't think it's fair to the person being accused of cheating if I cancel the bids, since both parties warred on it. But I'm afraid the person will refuse to pay up, or hide his comment. I did tell him he would no longer be allowed to participate in my auctions, and I would report him if he did so, but I'm still worried.
EDIT; The person who was bidding was NOT fake bidding, the other user was just claiming such. He ended up saying some stuff that hinted he would scam me if no one out bid him, so I banned him from all future auctions and rehosted the auction due to the fact that he had bid in all slots, and it would mess everything up.
I had no net, sorry this is a late edit.