Or buy the Sakic jersey i have for sale :-P
I'm pretty good in the jersey department, if you were to link me to one you were interested i can usually tell...
Generally speaking, if there is a fight strap....its fake.
Also, check if they have any other jerseys for sale, if it is hard to tell on one, see if any of the other jerseys look overly fake.
If it is $99 and a Premier jersey, that would seem less fishy, but if he is selling a "Authentic with fight strap" for that much....i would say no
If you want to buy a fake for the price that guy has probabaly bought his fake
check out
www.jerseyb2b.com
They have a huge selection of fakes and most of them look pretty solid, i am pretty sure he has Sakic too