I'd like to chime in with a question & comment. I have never understood why a buyer's premium is attached to these type auctions. I have to pay an additional fee for the right to purchase an item? Where else in society does this apply?
I can't think of one. Say what you want about Ebay, at least it's a simple "pay what you bid" system. And 17.5% seems ridiculously high. If you want $117.50 (for a $100 card) just make the minimum bid $117.50.