I have a car buddy who sold his Daytona at one of the big auctions and from what he said, you the seller are at their mercy. His car was sold and bought by the auctioneer company for way less than what it should have. Supposedly it did not go accross the stage at a very good time.
Also, he said the contract he signed was thicker than an LA phone book.
I have heard similar form a guy who sells Corvettes all the time. From what I have heard, I am not sure I would use any of them under any circumstances.