The buyer and seller always pay the same premium. I had heard it was 10% on both sides of the deal in the BJ auctions. But I see the 8% number bandied about in this thread. Not sure where that came from. I doubt BJ auctions would have reduced their rates.
But to answer the question, yes, the seller pays a premium, as well as the buyer. Except....the charity auctions, which have no premiums.