BaT has a buyer's fee of 5%, with a cap at $5000. The seller's fee is $99 to post the car with your own pix, and $350 for them to do the pix. They assist in the write-ups. They want the descriptions to meet a certain standard.
The seller chimes in, real time, on the discussions and questions that are posed, usually hot and heavy during the last few hours of an auction.
You can set a Reserve, and well as drop the reserve during the auction.
I agree that paying someone a handling fee when you buy a car goes against my grain! I recently bought a $30K car at another auction, and the fee was 10% ($3000 extra!!!).
With BaTm however, if the car you are bidding on does not sell, they will give you the seller's email and you can negotiate a post-auction transaction between the two of you, with no fees involved.
I'm planning to put my car on there for a $99 trial run -- but will be in a few months after I have other things sorted out with the car.