I recently placed an ad up on Craigslist to sell an extra iPhone 4S AT&T model off my family upgrade plan. Buyer was generous enough to have me stop by his place and he agreed to pay me without haggling on the price. Now next day he demands a refund saying the phone was not unlocked and he thought all AT&T iPhone 4S are unlocked etc etc. He has called me 24/7 non stop requesting and refund and even threaten to sue me in small claims court. Is it my fault for not telling him the iPhone 4S was locked? Should I refund him? He even tested the phone to make sure everything turned on etc. Help please. Thanks