This is wrong info! I have factory unlock and its display like regular other iphone! Only thing you can really test if its really unlock is making sure its on latest firmware and baseband then try 2 different carrier's Sim and make sure both of them get signal!
If you really want to be safe!!! Upgrade the iphone firmware before you give him the money! if its work after testing then you are good to go!
edit: You stated "SEALED" Just bring 2 different carrier sim! I find hard to believe its unlock and sealed at the same time! lol good luck!