In order to encourage more users to participate in bidding, we have an auction dividend mechanism. Whenever a bidder place a new bid, the previous bidder (if there is one) would get 20% of the bid difference as auction dividend. For example, if Alice places a bid of 1,000 BUTTER, and Bob places a new bid of 1,100 BUTTER, if Bob's bid succeeds, Alice would get 20% of the bid difference, which is 20 BUTTER in this case.