Actually those numbers are for Christie's.
Sotheby's website publishes their commission structure.
http://www.sothebys.com/help/faq/faq_duringauction.html
A little higher but no where near what Monte was saying.
If you'll notice though - their commission is charged to the buyer based on the tiered commission structure and not from the seller's earnings.
Christie's commissions are here:
http://www.christies.com/howtosell/termsofsale.asp
FWIW, in defense of cutting special deals. I contacted Moniker last year about a 6 figure buy and wanted to see if they could lower their percentage for escrow on it. I was told their percentages were firm. I don't know if the same is true for domains that are auctioned (ie the referred to 'preferred' pricing) but I can't imagine it would be given that they lost a several thousand dollar commission on a relatively easy transaction because of not budging.
