Signing up is free. To be a seller you'll need to register a credit card with them or some way to pay seller fees. There is a small listing fee to put something up for auction, then another small % once it sells. The amounts will be determined by a couple things such as starting bid amount and final price once the auction ends. If something doesn't sell you can re-list it and not pay a second listing fee if the item for auction sells the second time around. You will pay your sellers fees once a month just like any other bill.