I agree with everything you said about auctions in general. Auctioneers are doing work and providing services, and that costs money. If you do it yourself, you deserve to make that much more of the profit.

What I don't agree with is the possibility of any situation where the auction house makes a sale and they profit but the seller loses money. As I mentioned earlier, since the auctioneer is legally an agent of the seller, this situation could cause legal problems in some places.

I'd be opposed to the opposite situation too, of course, but that's not a thing that ever happens.