I don't see ethics being involved. It's not uncommon for a consigner to bid on his own lot, and if he wins it, pay the commission. I don't think eBay allows this, but many auction houses do.

If I were competing, of course I'd rather have the lot at a lower cost, but this is an auction; your cost is the under-bid, plus a bid increment, plus commission. Just the way this selling method works.

Bidding up your lot and then withdrawing your high bid is not allowed by any reputable auction house, eBay included. We'll have to see if that's what seller has in mind.