Many sites offer private auctions (Biddingyard.com, eMaja.com, BidPigs.com). First, what is a private auction?
Private auctions limit that amount of bidders that can participate in that auction.
How do you participate in a Private Auctions?:
Private auction rules vary site to site. At some sites it is free to participate, first come first serve if you will. At other penny auction sites you must use bids to secure a seat in the private auction. The participation cost might also vary auction to auction.
Why participate in a Private Auction?:
Since there are a limited amount of bidders, there are less members to compete with. Less competition means a great chance of winning.
Why should you not participate in a Private Auction?:
Private auctions usually attract experienced bidders. If you are not an experienced bidder, you should focus on open auction until you become experienced.