You're right about the neckline being a giveaway. The embroidered NFL Equipment logo is one of the better fake ones I've seen, but there are enough subtle differences to tell it's fake.
Aside from the neckline, for me the most obvious thing is the jocktag. It's a 2007 jock tag, and some of the legit ones did not have the space in "NFLPLAYERS" so that on it's own wouldn't be enough to give it away as fake, but compare the NFL Equipment logo on the jocktag and the shape of the "4" to the legit ones:
Definitely not the worst fake jersey I've seen, but fake nonetheless.