[Michael B]

There actually was a legitimate reason to do this. Back when you could view who was bidding on auctions you would want to protect the identity of the bidders. This was not just to prevent people from detecting shill bidding, but also to prevent revenge or adverse bidding; i,e. I know you are bidding on an item that you will pay any amount and very few other people are interested. I bid on it, even if not interested, just to force you to pay a higher amount. As a seller you would want to maximize your auction, but if the original person detected this and rescinded their bid you would lose out as the revenge bidder would then rescind their bids. It may also discourage the offers to end the auctions early.

As a seller of a popular item it would also help increase interest and attract more bidders in another way. I collect an item, but I see that Leon, who has more money than Moses, is also bidding on the item. He always wins any item he bids on so why bother bidding. If I cannot see who the bidders are I may bid and hope that Leon missed that listing. Most sellers may not recognize that, but I am sure some do. I know when I sell items I see bids from people who I know will pay any price and others are wasting their time, but they bid anyway. I recognize who will pay a good price and who the bargain hunters are. I will actually have listings for both types of bidders.

Full disclosure: I have never had a private listing and never would. I have never ended an auction early to sell the item. That is not honest.