Typically such listings -- particularly for expensive, unique items very often found in Japan -- are put up by professional brokers that do not actually possess the item in question. If the item is purchased through such a listing, the broker will then attempt to purchase the original and arrange to ship overseas to the eBay buyer.
Scammers also use the same basic technique, except the scammers do not actual buy or ship anything.
You can usually tell if the seller is a broker or scammer by examining feedback. Brokers tend to have a lot of feedback for selling such items, with possibly a few negatives or neutrals for cancelled orders (when the broker was unable to obtain the item and it was sold elsewhere). Scammers have little or no feedback for major sales at all -- or possibly feedback for sales of keychains or trinkets to build a false history -- at least until the negatives start rolling in once the scam item delivery dates begin to slip.
While it is against eBay policy for a seller to list an item not in the seller's possession (or under contract to the seller in the case of a drop shipper), eBay does little or nothing to seek out such listings in advance or to prevent them unless there are problems reported by buyers.
Private listings protect identities of all bidders -- but eBay sees no reason to hide your bid from you when you are signed in to your account. Other bidders cannot see your username, though, just as with any eBay bid. Private bidding also hides some information on the feedback page.
Be careful when bidding on private listings; always check the seller's feedback page, and if you cannot see any information about other previous sales, you cannot tell whether the seller is selling similar items of comparable value, or just getting feedback for selling keychains in order to appear legitimate as a set up for a scam.
