How to delete a sale in MarketPress

A customer purchased a product and used Google Checkout to pay. Her payment was declined. A couple of days later, she went through the process again, and completed the purchase.

Now I have a "sale" that doesn't exist.

How do I get rid of the non-sale transaction and revert the inventory to the correct amount. (Obviously, the plugin shows one less item in inventory than actually exists, because it recorded both sales.)