FYI there are fake memory cards, fake batteries, fake chargers, fake HD drives, fake CD/DVD drives, fake MP3 players (iPod, Creative), fake PCs (IBM, Compaq etc) and even fake notebook PCs (Lenovo etc.). Mostly from China.
So if they can make fake Lenovo notebooks, and even imitation iPods, what's so hard about making a fake memory card? Just print the Sandisk/Lexar logo and stick it on... print a serial no. at the side of the card. Afterall, all memory cards of the same type have the same form factor.
And the fakes I'm talking about are not cheap imitations. They're well made and almost impossible to tell apart - only the service techs could do so and only by checking the serials.