At auctions such as Barrett J, RM Sotheby's, LBI Ltd, and such..

..how much, what's the %, generally speaking, is added to the hammer price for Auctioneer's commission and fees? Does it vary a lot?

I'm negotiating a private sale of a rare car. The seller and I are both looking at comparables. A very close comp was recently auctioned for US$28,100 by Sotheby's "including commission and fees". I guess my seller can argue that those costs are part of the buyer's total cost to acquire the car, and that cost is part of the value of the car - so $28,100 is fair asking price...

..That seems logical, but no one adds the buyer's cost of shipping it home... plus insurance, or other "soft costs"?

Honestly, $28k would not stop me from buying it, but $25k isn't being unreasonable either. We are not arguing, we are just being as honest as we can.

I'd love to know what typical 'commission and fee' percentages are, and or any examples where commission and fees are NOT considered part of the "value" of the car..

Like... in Hemmings Muscle Machines - their Auction Results column shows Bid values as a market indicator - and I don't think that includes comm & fees.

Thanks for your thoughts.
- Art