And they should be.
And, if Amazon's entire supply chain is filled with counterfeits, all the more reason why Amazon should 1) reveal who the seller really is, or 2) be liable for the 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.)
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.