You can find the full rules at Axis & Allies ForuMINI :: 12-7-Games Reverse Auction-W@S Base Set & Task Force. But, here are the basics. All singles (rares starting no less than $7 and commons/uncommons no less than $@) from the Base Set and Task Force are eligible. Every 24 hours their price decreases by $1. All bids must be publicly posted in reply to the linked to thread on the ForuMINI. Shipping is $2.50 and no more than one 1 item per ForuMINI member (not per account, per member).
If you participate in the reverse auction, then please let 12-7-Games know that you found out about it here. They’re our sponsor and they like to know where their customers hear about them. Good luck!