Ask HN: How to safely buy a domain?

I have contacted a domain owner through his registered email, and offered him a certain amount of money for the domain. He accepted, and instructed me to pass the amount to his Paypal account, in exchange he will transfer the domain on my name. I was wondering whether there is some sort of middleman to ensure the domain transfer? Maybe Paypal can insure the deal? I know they take a lot of measures against frauds.

Thanks for any suggestion.