We have confirmation of this occurring on Fanatics Collect BINs, where sellers are “selling” their card to themselves or a friend to manipulate CardLadder prices and Fanatics Collect consignment rates. If they own multiple copies, they win in the end. If they lower the fee for a multi-thousand dollar sale when relisting the original card, they win in the end.
It is not a big stretch to suggest that it’s happening on eBay consignment auctions too.