yeah, i agree someone who is a scammer, or intend to scam would not message back and forth. his buyer most likely will ask for a refund, and return the ps4 to him.I don't mean to kick you while you're down but if losing the $400 puts you in bad financial shape, you really shouldn't be trying to get in on the high risk flipping scheme. I rarely dropship items but I would only offer to guarantee any item if I was the one to handle the shipping myself.
As mentioned earlier, as long as he's an honest guy you'll get your money back in the end with minor loss. The fact that he has messaged you over 50 times makes me think he's just a a panicked buyer that realized he overpaid for a PS4. If he was a scammer I think he would have simply waited it out and opened the case on you without such obvious angst and anxiety. Good luck with that.