I mean, quite a bit of that stuff people pay premium for is already counterfeit even at stores like whole foods. I don't know how common it is, but it does exist.

Amazon probably wouldn't help much though yeah.

My complaint is not just that counterfeit exists, but Amazon's lackluster response in dealing with it (here's your refund; now GTFO). Secondly, I'd guess that WF may have 1 ~ 2 suppliers for a given product, but Amazon may have hundreds, if they eventually allow 3rd party sellers. So they would have a harder time vetting their suppliers just by numbers alone. Finally, Amazon's warehousing policy of co-mingling stocks from different suppliers exacerbates the problem further.

there are third party sellers on amazon groceries?

The system would seem setup to allow it, but at the moment there are not.

Yes. But groceries and anything that expires is not commingled so if you buy from Amazon you get Amazon's inventory

They're not co-mingled yet, but there's no assurance that they won't in the future. And if / when they do, they're unlikely to forewarn you.

I can see “Amazon Farmers Market” now...

That'd be a nice feature. Creation to Shipment handling logs. Know which field(s) you food came from and what lots/etc.