I noticed an issue where if there is only 1 item in stock and two people try to purchase it at nearly the same time, both people will be charged for the single item.
Basically, if you have two people sit on the final confirmation page, the first person who clicks the Confirm Payment button will get an order confirmation page and an order ID. The second person will be redirected to a blank shopping cart, but they will still be charged via paypal. In the Manage Orders section, both show up, but the one who was second will have their Items set to 0 instead of 1. Confirmation e-mails are also sent out for both orders, but on the second order, the item is listed as “Item * 0 = 0.00”.
On clicking Confirm Payment, it seems like it should do one final inventory check, or else for limited quantity items and a high traffic site, there will need to be refunds issued and potentially unhappy customers.
Thanks for looking into this as the inventory control is fairly important for an upcoming project I plan to implement via Marketpress.