If the price are below $50, it is likely to be fake. Some common giveaways are 1. unusual colours or colour combinations 2. box doesn't look like a Nike box or the Nike product number is not correct on the box 3.plastic soles instead of rubber ones.
Below is a website that sells the real thing. This page shows the cost of each pair to be well over $50 :
http://search.nike.com/niketown/?loggedin=false&Ntt=nike+shox
Other authentic sites include:
http://www.finishline.com/store/index.jsp
http://www.pickyourshoes.com/size/nike_shox_basketball.htm
It's best to buy shoes from places that stake their reputations on authentic merchandise. You risk buying a fake if you go to discount places.
Here is a website that talks about fake shoes:
http://www.instyleshoes.com/common/fakes/article1.htm
You could email them for speficic details.
I hope I have helped you and that you will accept this help.