It may be a scam, and it may not. I have sent thousands of $ friends and family after I convinced myself the seller was up and up. But if I am even a little bit unsure, I take actions to protect myself.
I suggest telling him the truth:
"I am uncomfortable shipping this item until I have been fully paid. If you don't want to do the deal, that is ok. I will refund your deposit. But I can not ship until I have full payment."
He will probably argue. Stick to your guns. Be ready to walk away. If he suggests something even more convoluted, refuse. The more complicated it gets, the more likely it is a scam.
There is no problem refunding the paypal payment. Paypal works by reversing the payment, It isn't a way to launder money. Now if you initiate a new payment to him instead of refunding his, that is a different story.
--Jerry