Other bidders' IDs are ALWAYS concealed on eBay, for privacy reasons. If you look at the bidding history for any item you will see that bidders' IDs are scrambled, with asterisks. Only the seller and the bidder can see their real ID.
Private auctions are a throw back to the time when this wasn't done. The only purpose they serve now is to make it impossible for anyone to view even the limited, anonymous information that eBay still makes available.
Private auctions are often abused by sellers to conceal shill bidding or other tricks to inflate the price, so be on your guard. A good precaution it lo leave your bid until only a few seconds before the auction ends, when sellers won't risk trying to drive it higher - in case they end up winning their own auction!
