How to tell if a micro sd card is fake or real

I have about 6 2gb sandisk micro sd cards that i got on amzon and 2 4 gigs and a 16 . Some of the 2 gb cards have different markings on them. How can you tell if they’re fake

if you want to make sure that the card you will purchase is genuine, but them from trusted retailers like bestbuy… if you already purchased one, then try calling sandisk support for authentication… their number is 866 7263475. i believe option 2 is the one for the memory cards.