Sports Direct isn't fake at all, they sometimes have really great items. Why they are cheap is another answer - Basically, I believe they buy old stock from companies and sell them on at a lower rate. Also, buying bulk items will decrease the price as well so all is well.
However, you say the Nike shoes are cheap. I have found many other items which are actually extremely expensive.
Everything is the genuine thing, we would be shut down if we sold fake clothing or footwear. We can sell alot of brands cheap because we own alot of the brands that we sell.
It's not fake everything is genuine. I bought a pair of Nike shoes a few months back from them. I think it's so cheap because the items are old stock/last season but definitely not fake.
How about ferrari??