Were you the original purchaser or did you get it secondhand? Hopefully the serial number didn't ping as reported stolen or a similar issue. Pawn laws are legitimate, as is a pawn record that law enforcement has access to and reference. I'm sure it's state-specific, but having worked previously in LE, this is a real thing.
Having worked at Gamestop and another similar store called Disc Replay I can say that pawn laws do vary state to state, but almost all of them will require items like game systems have a valid serial number. If he got the PS4 secondhand there is a good chance it could have been stolen and is being flagged, but usually, that wouldn't prevent them from taking the trade. Usually, we'd take the trade in order to obtain the persons information so we could report the info to the authorities and they could investigate it.