How does he insure he doesnt get scammed?
No idea about that. But he sells Bitcoin in exchange for both Paypal and OKPay. Charges a premium of 17.5% if Paypal is used, and 0% if OKPay is used. That means he expects at least some of the buyers to scam him.
Must be something else to it. I imagine scammers will just take advantage of this all the time.