Keep it in the Pm's. If the account was highjacked they wouldn't be able to hide that beyond a deal or two before being outed. It's less likely they swiped an account and you are the first victim. Through any other form of communication, you lose that edge.
Search their member name here. Both "everywhere" and "in this forum" while you are in the exchange and the good, Bad and ugly. Look for complaints and previous threads for sudden changes in communication, requested communication methods, language fluency, etc.
Download and image search the photos provided. See if they show up other places at other times. Does it appear they could have downloaded and used someone else's pics?
Insist on a real time photo with the username, date, time and state of residence written on something included in the photo. Check the time to proper timezone.
Insist on G&S and use a protected CC from your pp wallet for payment.
Anyone unwilling to do these things shouldn't be considered for a transaction.