We were involved with one such "Auction". After attempting to gain a contract through normal means, the prospective client informed us of this online auction. A date is set and all parties involved are informed of the limited time window to bid against each other.
No other bids can be seen apart from your own and the lowest. Prior to the auction a tender form must be completed in the usual way with all your details which is sent directly to the prospective client.
There are certain rules and T&Cs which I would advice you pore over before any bidding: One of which will be along the lines of the Client has the final say on whether to accept the winning bid or stay with the incumbant company. This is the one we fell for on our one and only online auction. We won the auction, but the client wanted a lower price so stuck with their incumbant company, who we beat in the bidding as they were higher than us!
Have a limit you wish to reach before you bid and stick to it. The pressure to change during the auction is huge as you are time limited and so is the urge to bid unnecessarily, so have a team of people involved ready to pull the plug.
It is a good experience but not one we will be entering into again as we won then lost. "Success" can lead to a disappointing result.
The link to the company who arranged our little venture was :
http://www.scanmarket.com .
This may have closed down so you may have to browse for Scanmarket (Scandanavian Company)
Be careful and check out validity as much as you can online and elsewhere as there are a lot of dodgy dealers out there, don't leave information on any of these sites which may be confidential.
Good luck,
Phil