Check the grommets. If the grommets are straight through the holes, that is a fake. For the real, at least all the newer PD or AD have the grommets that are flatten out at the inside of the hoop. It looks as if it is made for letting the nods of the string to rest there.
Hope you understand what I'm taking about.
I got two AD off the auction site about 2 months ago, I deemed that they were fake because it felt like head heavy, too much vibration, and the grommets were different. I returned them to the seller under Paypal's protection program.
One more thing, if the hologram authenicity label on the racket displays some chinese words, it is a fake too. My friends in Hong Kong bought the real one from store, and the real one has the hologram without chinese words. The fake ones that I got from internet displayed the chinese words.