In the coming days, users in the US, UK, Australia and New Zealand who are over 18-years-old will see a new shop icon in the bottom menu of the Facebook app. This will load a selection of photos of items that people in your general location are looking to sell. It also includes a search function, if you're looking for something, specific and results can be filtered by location, category or price. If something catches your eye, Facebook will list the name and details of that product, a profile photo of the person selling it and a loose overview of where they live.

Although Facebook already lets Messenger users send payments, the company categorically states that it is not performing the role of a retailer or auction site: "You and the seller can work out the details in any way you choose. Facebook does not facilitate the payment or delivery of items in Marketplace." That also means it won't charge users for listings, giving it a distinct advantage over eBay and other app-based buy and sell services.

With Facebook now counting over 1.5 billion users, sites like eBay and Craigslist will be watching Marketplace with keen interest. Sure, it's currently only available in four countries, but with little to no oversight over sales and payments, the company is free to take it to new markets at will. Facebook says it will "continue expanding [Marketplace] to additional countries" via its iOS and Android apps, and will make the service available on the desktop "in the coming months."