A reverse auction is where instead of the bids starting low and increasing, the initial bid amount starts out high then each bid is lower than the current bid, so the winning bidder is the person who bids the lowest amount. Reverse auctions can be used when several suppliers are competing for business, and they all try to offer the lowest price for the product or service so that they can secure your business.
Bids cannot be negative, the lowest possible bid is the minimum bid increment.
To setup a reverse auction item, when you create your auction items you must set an initial opening bid
In your menu item auction options set Reverse Auction to Yes.
Warning, all items displayed through that menu item will operate as a reverse auction, so if you have normal auction items ensure that you limit the reverse auction to only one specific category of items.
Now the default next bid is the current bid minus the bid increment.
For reverse auctions, you cannot bid higher than the current bid