[Karunamon]

Memory cards / thumbdrives are the canonical example here, I think. The fakes are plentiful, and comingling ensures that you are playing roulette every single time you purchase one, and the fakes are good enough that they'll stand up to visual scrutiny unless you know exactly what you're looking for, and sometimes not even then.

[TakerofVita]

I remember for a brief period where there were 256 GB micro SD card listings on Amazon...before there were any real ones released by anyone.