It's really quite easy the air bubble on the sole at the heel on cheap fakes are empty you can press it in with your fingers whereas on genuine trainers you can't even move the bubble because it is full of air this you can't check until you have got them but make sure the seller excepts returns if your not happy and not just only if goods are faulty as most do that sell fakes.They sometimes come in mad colours which you have never seen in the shops which can be a giveaway,however some High street Retailers (JD and Footlocker) have "Exclusive Colours" made just for them so watch for this also. You also have to ask yourself why they cost a quarter of the price they do in a store?Because they are fake?Ask the seller if they come with the arch supports because all Nike Running shoes come with the 2 Red doublesided foam supports and i guarantee 90% of the copies on Ebay don't this is also a real giveaway just BEWARE there are a lot of people trying to get your money so do your homework first and make sure you ask the correct questions.Genuine Ebayer's will answer your questions all day long but the con men with the fakes just treat you like idiots and try to insult your intelligence with transparent answers,if your not sure then don't buy them don't part with your cash for fake shoes.
Beware there are a few sellers with Airmax 95's which have a rectangular badge on the tongue of the trainer,BEWARE Nike never made them like this EVER. The Airmax logo is an oval shape on the tongue of the shoe.There are a few sellers with these now and some have more than one account, beware guys they are really bad copies that don't fit correctly and fall apart.
****UPDATE**** 9th Septmeber 09
Please be aware that some of the boxes they are being sent in will have a web address airmax.com this is not a site related to Nike but in actual fact a company that deals in heating and ventilation, you think they would at least have checked this first. Another dead giveaway as to their authenticity.
Over the last 6 months i have looked at 324 listings for people and only 31 were genuine so please please please watch out there are more counterfeit shoes than there are genuine on Ebay.
****UPDATE**** 8th December 09
Please beware the shoes with the rectangular badges are back on Ebay, after a good couple of months with hardly any they are back. People wanting to sell their fakes to unsuspecting ebayers looking for a Christams bargain no doubt.Their are a few ebayers who are selling them innocently without knowing they are fakes but not many. Remember all genuine shoes have an oval stitched badge. Have a nice Christamas and don't get ripped off.
!!! JULY 2011 !!!
There are a few wild colours on Ebay for sale,combinations that were never produced by Nike..Listings with more than one size and with spare laces are also a NO NO. !!!! BEWARE and be sure before you buy !!!
Always ask as many questions as possible if your not sure.If they are new then the seller must have some proof of purchase for you to check. Ask and see what they say.
Hope this helps.