As disclosed in this thread:
http://forums.spiralknights.com/en/node/59270
When you win an auction and receive a mail from Auction House, if you do not press the "Accept and Delete" button within 30 days, the mail will be deleted along with your item, and you would not be refunded.
This is insane. You paid for the item; why should the item be deleted? For mail between players, if the mail is not accepted the item will be returned to the sender. For auction house the sensible default action should be to accept it, not throw your crowns and item away.
Please fix this!
"Herp derp, I will bid on this derpbillion crown item off auction then go to Russia for a month."