When I took over the online marketing for coffee company Devil Dog Brew, I wanted fans of DDB’s Facebook Page to be able to purchase coffee without leaving the page. The solution I found was Payvment. Payvment is free to sign up and only requires a paypal account in order to accept purchases.
Adding items to the storefront is extremely easy and allows for attributes to the items (i.e. shirt size, color, etc.) The only thing people may have a problem with is shipping. You can only set shipping cost to a flat rate.
Overall, Payvment is a good solution to selling products on Facebook.