For me I can always tell right off with the scales. Fake scales have the little indent details and are a little glossy. Authentic scales are flat and not glossy.
http://pages.ebay.com/link/?nav=item.view&alt=web&id=121481832120
That is the seller he has a lot of flyknits going up using stock photos from rep sites. I've been reporting him as he says they're real direct from Nike and he has receipts when I ask about them but shows no receipts or box...
GF ordered me some shoes for my birthday.. She got them on eBay and was pretty upset with them and showed them to me early.. The guy lied to her told her they were from the nike store etc etc.. typical. I've been arguing back and forth with them they are saying I have no proof they are fake...