another # to look at is the seller's net $ figure at an auction

$30,000 hammer price
$33,000 buyer pays (hammer + 10% buyer's fee)
$27,000 seller receives (after 10% seller's fee) - any additional consignment fees

$6,000 auction fees + any additional consignment fees

seller & buyer will both have costs associated with transportation, lodging & registration to attend the auction

after a good auction weekend, the seller is going to end up with $25K in his pocket for his $30K collector car!