On a whim I once bid on a "collectors" type Switch game. Me and someone else raised the price near the end of the auction. Not being used to eBay bidding I wasn't ready near the final seconds and got outbid.

A couple of days later I saw the same item relisted. I wouldn't be surprised if the person I was bidding against was just there to pump the price for the seller, or was an alt account of the seller. Obviously against eBay's TOS but I'd be surprised if it didn't happen.