When you accept a bid on a player via the list of incoming bids an auction will be started. In case you have other incoming on the same player these that have the same or shorter duration demands, these bids will also be accepted.
Club A has made bid of 50 Credits and 100 Credits as auto bid. Klub B has made a bid of 20 Credits and 120 Credits as auto bid. The seller accepts Club A's bids. Now, Club B will be the high bidder with a bid of 101 Credits. This is because Club B's auto bid was higher than Club A's.