[KMnO4]

Important thing you should be aware of: not all counterfeit cards fail a format/f3 test.

I recently bought a very expensive Sandisk Extreme UHS-II V90 card from Amazon. It passed without any issue when doing a full capacity check, but was still fake because they were using slower (150mb/s vs 300mb/s) flash.

The average user[0] would never know, because it was definitely “faster” than other cards and maxed out the UHS-I reader in my MacBook Pro. I returned it and bought from my local camera store (Henry’s) and the performance difference was very obvious.

[0]: I guess you could argue that the average user wouldn’t be buying a $200 V90 card, but I still think you could fall victim to this if you didn’t explicitly own a dedicated UHS-II reader.