on 02-21-2016 08:15 AM
First, set your Buyer Requirements to as strict as possible, i.e. no paypal account, 2 non-pay strikes in the last year, live in countries I don't sell to.
Second, sell your phones fixed price with immediate payment required.
Those two things will stop the scammers without paypal accounts and buyers outside the US.
As for a buyer claiming phone is defective, always reply to the case with return for refund. Never give a refund until you have the item back.
You may get a return that is not the phone you sent. There is not much defense against that although you can report the scammer to ic3.gov, to the USPS for mail fraud and file a police report with both your and the buyers police. All the reports will do is get the buyer on the radar.