There is no problem at all in bidding a player a little more than he's supposedly worth. Some of these estimates are really WAY off.
I do think GMs can have acess to the bids that a player receives, if need be. So I don't think getting caught in a bid war and overpaying for some player is an issue too. It may be a little stupid to do that, but I don't think its illegal.
In reality, there must be a huge disparity in the player value and the bid for it to be considered cheating. I wouldn't worry if I were you.