There are lots of people from Asia, mainly Hong-Kong I see, that sell fake shirts online.
Bigger problem is, they have contacts across Europe for example who sell shirts on forums or local auction sites similar to Ebay, where there aren't rules like those that state that you can't sell fakes and promote them as "Nike, Adidas, Puma etc" only "FC xxxx Home Shirt 2009/10" for example. Still, there are probably many on ebay that advertise them as authentic and some might not even know that they're possessing fakes.
For one, Nike fakes are in my opinion more easy to spot, they're harder to fake than Adidas IMO, there are many indicators if they're fake and the material is harder to copy perfectly.
Second of all, I see that ex-sites that sold them from HK as fakes have gone down recently, maybe there are others, but they sell them cheaper than those guys in ebay. There are many who sell fakes for "150 RON a piece with or without printing" in Romania, probably buy them for 10 euro a piece ( 45 RON ) + delivery which shouldn't be expensive if they order 10+ at least each time.
I have an Inter 2007/08 + Champions League version + Ibrahimovic 9 Printing. My intention was to buy it along with the centenary away and sell them, I bought them 25 euro a piece from a guy, didn't know they were fakes, resold the away one for 70 Euro and later found out they were fakes, the home one I couldn't sell but the profit was there.