You're going to get different opinions on the practice of buying back items; but to answer your question, you'd need to be the high bidder during the live auction and then while settling up at the end of the sale, you'll be charged $10 as a "buy back fee".
To clarify, you can't let someone else win the auction, then decide later to buy it back, you've got to be the winning bidder.
I've been going to arcade auctions since the early 90's and my personal opinion is not to buy your items back. For starters, there is the cost and time involved that you'd have to make up the next time it's up for sale. Secondly, I'd only consider it if an emergency happened for example the Addams Family pin you brought, died before the preview and you're going to take a substantial loss.
Some professional sellers buy back half the games they bring to auction, and that usually upsets the collectors that bid on them. Right or wrong, it's the way they're run.