transfer process

I have one Domain auctioned lets say i agree price with a buyer, whats next ? - Would he pay me first, lets say through paypal, then i would give him the authorization code or i have to give him the authorization code before payment ? - What's the surety that the buyer would pay me once he has...

I have one Domain auctioned lets say i agree price with a buyer, whats next ? - Would he pay me first, lets say through paypal, then i would give him the authorization code or i have to give him the authorization code before payment ? - What's the surety that the buyer would pay me once he has...