According to an unverifiable source around 30 percent of all SD-cards offered by non-official dealers are faked.
If you purchase a card from such a source a thorough after-buy check is mandatory (in all other cases highly recommended).
Check for faked speed specification:
- Fast cardreader + PC + a benchmark program like CrystalDiskMark (Windows) or Blackmagic Disk Speed Test (macOS).
You only need to run sequential R/W. Compare with benchmark runs from reliable sources like
www.cameramemoryspeed.com Check for faked capacity number:
- Cardreader + PC + h2testw (Windows) or f3/F3 QT (macOS)
If capacity info is altered by some crook you will get serious data corruption because cam will overwrite data recorded previously if physical storage limit is reached. Cam's firmware (and your PC, too) rely on card's info set to be correct and will not check if data set numbers and reality match.