A long time ago (15 years?), it was possible to view who all the bidders and sellers were on ebay users' history pages.
After finding I had been ripped off by a shill bidder (seller using another account to bump up their prices) I started using this facility to check out sellers before I bid on things. For example some sellers' items all had bids from a particular account which was always either the final or penultimate bidder, and those where it was the final bidder were always relisted a week or two later.
Several times I saw items sell for absolutely ridiculously high prices like the one you describe, and each time it was due to the seller accidentally bidding on their own items from two, obviously connected, accounts (instead of one). Generally one early bid and another in the last ten seconds - on most of their sales both these would be from the same account. The items were subsequently relisted...
Ebay removed this bidder / seller disclosure facility shortly after a widely publicised case in which a seller was successfully prosecuted for fraud for shill bidding. They obviously didn't want anyone to see how widespread the practice was.
