This is from people studying the price trends of outputs compared to those of inputs. If some sort of oligopolistic pricing is happening you'd expect to observe price trends of outputs change as concentration increases.

I'm not vouching for their methods or conclusions. That's just some context that I happen to have access to.

How would the general view know? In  most collusion cases we find out after someone blows a whistle or takes an offer in a case. 

TNStacker

I've done some work on related topics. While it's certainly true that concentration is increasing throughout the ag sector, the general view seems to be that there is not much evidence to support monopoly pricing.

Undisciplined

econ

Grocery Store Price Gouging?

my point is less competition leads to collaboration, whether or not a formal cartel is formed. A natural, informal organization forms due to game theory. 