It used to be the case, that when you were either buying direct from Amazon or FBA, it provided some peace of mind. Today it is a lottery. If you haven't come across any issues then you are either too trusting and/or probably not conducting basic tests to check if the products are indeed genuine. As a demo, I would dare anyone to buy a microSD card randomly, and then put it through h2testw/CrystalDiskMark to check for anomalies.