Once the player is placed on the market for a particular value (let's say $XXX.XX), players bid for him, with bids ranging from lower_value = $XXX.XX - some amount (don't know how the amount is calculated exactly) to upper_value = XXX.XX + some ammount. Once there are at least 5 bids, the 6th bid takes the bidding into the next stage, where the lower_value and upper_value are increased and the previous 5 bids are discarded. The 11th bid will do the same, and so on. There is a cap on the bidding rounds (not sure how that works exactly), where on the last round, the lower and upper values aren't increased any more and you can get any number of teams bidding.
That way, a player might be placed on the market for a certain value and there can be an initial upper value close to 2.5 of his market value, but if there's a lot of demand for that player, people will be allowed to bid more.