In December, Facebook started testing classified ads and now you can search across groups (public and subscribed to) and within categories. This feature should be released in the next few weeks with an a sales group link in the left pane. Users can post items by going into groups and selecting on 'Sale and Item' next to 'Write a Post'. Users will need to enter some information similar to an eBay auction to list their item for sale to the group.
Facebook is hoping to compete directly with eBay and other classified ad sites that sell items online. The advantage is that you can see how you are buying a product from and there are no fees, but the selling history does not exist at this point and there's no built in protection.
DJ-Classifieds - IFTTT and Facebook pages integration