I checked the terms and conditions on that for some clarification and here's what I found 5. Shipping and Pickups You agree to respond to all valid requests to ship or pickup items from closed auctions in a timely manner. Failure to promptly arrange for shipping or pickup of items may result in a forfeiture of credits. You agree to work out shipping expenses with the auction winner outside of the Site. Listia is not responsible for any lost shipping expenses and cannot refund or help recover shipping expenses for any reason, including lost or stolen items, damaged items or non-shipment.
What that boils down to for me is that I'd have to figure out some way for the winner to reimburse me for the shipping cost. I don't want to make this complicated. Free shipping.