You misread the comment you're replying to, I think. empath75's claim "Amazon’s entire supply chain is filled with counterfeits" is intended to mean that parties other than the seller—such as warehouse employees, delivery companies, importers, etc.—are also inserting counterfeits into Amazon's supply chain, such that even products "sold by Amazon" in the strictest legal sense, can potentially still be counterfeits.
Given this, customers should already have been wary of purchasing from Amazon, enough that finding out that they're often purchasing from third-parties shouldn't further affect their opinion (i.e. they should already have as low an opinion of Amazon as if they had already known that, because of the other supply-chain problems.)
Most people don't have that opinion though - things brought through Amazon are viewed as being vetted and high quality when compared to items through eBay or Wish - Amazon has made no effort to disabuse people of this conception and I personally think they've worked actively to downplay the role the third party plays in product delivery.
I've also always been a bit curious if amazon might be liable for defective products shipped through their warehouse by virtue of the transfer of custody alone. This sort of business model is quite new (it's worlds different from a flea market) and there are several interesting commercial responsibility questions around it.
Given this, customers should already have been wary of purchasing from Amazon, enough that finding out that they're often purchasing from third-parties shouldn't further affect their opinion (i.e. they should already have as low an opinion of Amazon as if they had already known that, because of the other supply-chain problems.)