From the BAT website
Seller
. The best place to sell a collector vehicle, period. $99 to list, no other fees for the seller, and a custom auction for your vehicle on our site.
Buyer
How much is the buyer's fee? If you win an auction we charge 5% of the final bid price on top of the winning bid, with a minimum fee of $250 up to $5,000 (5% of a $100,000 bid). The fee for sales higher than $100,000 is capped at $5,000.
And isn't there still a Buyer's premium paid on Bring a Trailer?