You never noticed an issue, that doesn’t mean you avoid getting counterfeit items etc.

But counterfeit products on AliExpress are commonplace as well. This is about getting bad products (which counterfeit ones not necessarily are)

Products can be defective or even harmful without you noticing.

Does your multi vitamin actually contain every vitamin it says it does in the dosage it should? For many things you really depend on reputation and outside regulations as you’re hardly going to send random samples to a lab.

Even reputable companies make use of this. Look into how often SSD internals get downgrading without changing the product’s label.

Which is why I don't buy stuff from there that goes into my body