The only way he can scam you in my opinion is if he somehow makes a fake trade on a Runescape Private server.
It's very worrying, you bring up a valid point. PlayerAuctions Customer Support is among the worst of any company in the entire world. I also don't think they will even forward you the pictures of delivery when he submits them, so you won't be able to point out the differences.
This is why you still don't buy things from randoms, even on PlayerAuctions. The PA system is FAR FROM PERFECT.

