Why? It's like ebay.
You set a maximum bid you wanna go to, someone else sets a maximum bid bid lower that that so it ups to his maximum bid + 1.
A bids 5k
B bids 10k
Highest bid is set to 5k+1 as in 5001
C bids 50k, highest bid is upped to 10001 gold as player B is outbid.
Player A rebids 25k, offer is upped to 25001 gold.
Auction ends, C gets the item for 25001 gold, seller gets 23 750 gold.
Everyone else gets his gold back and C gets 24999 gold back since he deposited 50k in the first place.