Sure they could, but with a proper approach to supply management, like the whole of the traditional sector is used to it gets caught. The lower quality switch would get caught in the random checks of incoming product in your first years as supplier, or rapidly from customer feedback. Then simply drop them as supplier.

Amazon would look far far better to their customers if they started cutting some of the crap as "not good enough to go in Amazon" and dropping suppliers for shoddy manufacture or too high a return rate.

There is a big difference between cheap, good value and all the world's unfit for purpose and counterfeit crap, for me anyway. They can pretend marketplace is separate, and outsource returns and customer service to marketplace sellers all they like. If I buy something dangerous or shit on marketplace I resent Amazon as much as the RNGFake4u brand I accidentally bought.