Although the process of selling on sites like Usell might be easier and less hassle, you get far more by selling your phone on ebay. I just did a price comparison of the iphone 5s 16gb, and usell offers a price of $260, while they sell on ebay all day long for over $100 more at $360. I am in the UK and this space is already very crowded, exactly the same concept as usell.