The only way to transfer cards between portfolio is via the eBay Trading Floor. Therefore, when two collectors agree to trade eTopps cards a private auction can be set up enabling the seller to allow only that person to bid on their eTopps card. The cards are transferred to complete the trade after the auction ends. Also: How to Set Up a Private Auction. Related: Trading.
In a private auction the buyer's names and e-mail addresses are not disclosed to the public. In addition, the purchases are not shown in the buyer's history. Private auctions are used in the buyer's identities need to held confidential because of the nature of the item being sold.
Is an auction where the bidders usernames are hidden, so that someone looking at the listing will not know who bidders are.