I've had a few instances where I have ordered a product that was listed as "Ships and sold by Amazon.com" and still received a counterfeit product. Only to go

I've had a few instances where I have ordered a product that was listed as "Ships and sold by Amazon.com" and still received a counterfeit product. Only to go back to the reviews later and see the "Most Helpful" review reports that their item was counterfeit as well. Anyone care to elaborate how this is possible? Surely Amazon is not doing this intentionally, are they just getting ripped off by their suppliers?