Use your credits to turn your auction into a Premium Auction after it has been listed! If you are eligible you should see a button on your auction page to do this. Sellers are required to have the Seller Wings badge for this feature.
When your auction is a Premium Auction the title of your auction will be bold in search results and you will also get a small Premium Auction icon next to it. Your auction will also get special placement on the search results and auction pages. The more visibility your auction gets the more bids you'll get!
The cost for Premium Auctions will change based on availability. There will only be a limited number of spots at certain prices so if you find it cheap be sure to grab that spot!