Create a Facebook Shopping Cart Solution.... that allows users to actually MAKE purchases through Facebook .... vs. being redirected back to the website.
Making the purchase through Paypal on Facebook vs. being redirected back to the website is one less click users have to go through, thus increasing conversions for the retailer.
I would gladly pay for that extra feature and I know several thousand Facebook savvy marketers would also. So please 1shoppingcart.... please develop a fully integrated Facebook eCommerce solution.
I know your customers will love you for it!!!