Trent: First, you are 18 years old to be on Listia. Second, the bids are done with credits that you already have. Third, if there is a shipping charge, you must pay it, preferably using your PayPal account when the person who listed the item sends you an invoice.
Fourth, if you list something, you are agreeing to ship it free unless you specify a charge, which must be in line with Listia Rules. Fifth, if you list something and you don't get the amount of credits you want, you still have to send it to the winner.