I once almosr bid on my own player for this reason. I wanted to upgrade at SG and put up one of my SG on auction. The bids were so low I thought I couldnt get better and was going to outbid. The bid went high enough so I didnt bid, and next time I will just set the minimum higher. I can see where someone might legitimately bid on thier own player.
It doesnt work much in your favor to try and jack up the bid, because if you get stuck with your own guy you lose on the taxes and for the next sell attempt its even worse. Better to set a mnimum bid at the lowest you will accept. If you think someone is trying to jack the price up, try and stick him with his own guy. That'l teach him :)