There's an online used bookstore (Estante Virtual) in Brazil that kind of does this, though obviously with books. It's a network of 9 million titles, all coming from secondhand bookstores throughout the country who have uploaded a list of their inventory. When I browse for a book, I can choose a local vendor and if I want, find out the location so that I can just go there in person if I think that's faster than Brazil's national courier services (as many times, payment to the vendor means making an in-bank deposit to their account).