I just won a bid on an used iPhone 4S for Sprint. The seller says it has a clean ESN in the information but after I won. I messaged him and asked for the ESN number so I can contact Sprint to double check. He sent me a message back saying once I pay through paypal he will provide the ESN number because it is a security concern to do it before and once I pay I will be covered by paypal and eBay. This doesn't makes sense to me. Is providing an ESN a security concern. Any thoughts will help.