Unfortunately counterfeit Nike trainers are big business and many people get caught out everyday when buying on ebay and websites which look like reputable shops.
Before buying Nike training shoes, do some reseach. Is the colorway an original colorway released by Nike? Many have never actually been released so this is the most obvious giveaway. If people or websites are selling OG colorways together with colorways never released, avoid like the plague. They will all be counterfeit.
Are they a trainer that has not been re-release by Nike recently, yet there are multiple listings on ebay all at a cheap price? They will be fake!
Upon instpection of counterfeit Nikes, there will be subtle differences in quality and production. When you put them on it may be even more obvious in other ways; they may feel tight, heavier than normal, not so comfy etc. Some people believe the trainers are made in the same factory as the originals which is why they are sometimes hard to tell if they are conterfiet straight away. Just remember, they might look a very good copy but the quality of the components is not equal to authentic Nikes.
Furthermore, if you sell Authentic Nike's on ebay, you may find yourself bombarded with unsolicited emails offering you to buy Nikes direct from a whole-saler. They will have a web-site and offer a variety of Nikes, alot of them never actually released by Nike in those colors! These are Fake!
What can you do? Well, Nike want to know. Seach the web for the counterfeit Nike email address, forward your concerns and evidence to Nike directly - They will investigate. (I tried putting the email address on this guide but ebay do not allow links).
Good luck bidding, remember these pointers and you should be able to get yourself the shoes you want and remember, it's not a bargain if they are fake!