No, even if you found a phone and tried to locate its rightful owner, you should not try selling it on uSell.com. Most times, the owner of the phone has already reported it as lost or stolen, so buyers cannot resell it.
When you use uSell to sell your unwanted devices, you are agreeing to our Terms of Service which state that, 'you are the actual legal owner of any and all property offered to be sold through the Site and Services and you are acting on your own behalf.' Any attempt to sell a lost or stolen device is a direct violation of these Terms.