The thing about these counterfeit DVDs, is that they are such exact copies, the only way to tell if they're fake is if they are professionally examined at a forensic level. So how would you know if you even had one, that's been laundered through a middleman or two?

There are quite a few visual signs of fake discs, it depends on how professional the manufacturing is. 

I'm not greatly informed about the quality of the copies this seller had, but I bought a second-hand DVD (not from the seller being referred to here, or indeed a seller I would suspect as being involved in such a thing), and it looked like a 100% genuine article to me. The sleeve insert was very good quality and gave nothing away, as was the picture disc. 

If it had actually worked, I would have been none the wiser, but it didn't so I took a closer look and knew within seconds I had a pirated copy then.

While it had myriad official looking run-out codes, it said Made In Hong Kong and the SID code was for a German manufacturing plant. 😉