[ferminaut]

I first ran across this scam in about 2002 with SD cards back when digital cameras were much more popular. I recall a vendor "proving" it was legit by plugging it into a computer in front of me and showing the SD card had 1gb of storage.

I'm sure the scam is even older than that.

[Gigachad]

There is a tool which can reliably detect this https://fight-flash-fraud.readthedocs.io/en/latest/

It attempts to write the full storage and then read it back. If its fake, the read will fail. It's also useful for detecting storage that has become unreliable.

[GauntletWizard]

Absolutely, but it may take multiple minutes or hours to detect; which you do have when you buy it off Amazon but not when you've bought it off a sketchy vendor at a flea market.