The unpaid item dispute is generally a manual process, and while it reminds the buyer they have an obligation to complete the transaction, it can't force them to, so if no payment (or arrangements to make payment / pick-up) is made, you are able to close the case four days after opening it to receive a credit for the final value fee charged on the sale. If the case closes without payment, the buyer will receive an unpaid item strike, and you can then relist the car if you wish.
