You can "buy from" a seller that provided 100% legit units and still end up with a counterfeit because Amazon threw them all in the same bin ("commingling"). This is the basis of the Daimler lawsuit: there were counterfeit items "sold by Amazon.com", whereas Amazon had previously gotten a pass because they weren't actually selling the counterfeits themselves.
Awareness isn't enough: even if consumers know that there are counterfeiters and other bad actors, they doesn't mean that they know who they are. This is in part because the review system is compromised.