To do a refund, the winner of the auction has to send you a request for a refund message and all you do from there is agree and give them back their credits
Im not sure what you're asking, once the refund message is sent its pretty self explanatory, you have to wait 2 days after winning an auction before you can send that "request for refund" message, if there is no reply to that message you will get your.credits back after 5 days if he does reply but does not give you back your credits you can contact Listia and they'll settle it
Scroll all the way down to the bottom of the page and right next to the buttons for the Listia apps there says "Contact Us" or if you have any general questions click on Support