I disagree. Payment methods...they have deniability. how bout western union. ? They profit daily and the Feds know this. They KNOW how sources do things. Don't think they don't. Never once in taking down a source then western union. You would have to prove in criminal court that they had knowledge of the illegal transaction regardless of the "profit" or not
It doesn't matter. The fed know lots of things and see lots of things they don't prosecute. That doesn't make them not actionable in court if they choose to. The govt often turns a blind eye to illegal activity if its reasonable, and there are extenuating circumstances or they just aren't that interested.
The govt is like any other enterprise. They have limited resources and manpower, so they don't go after everything. They need agents, lawyers, personnel, etc to handle a single investigation of this nature. So they don't go after all of them. They have to fight the fights they think are worth fighting, the ones they think they can win and that's often based on political priorities at the time in question.
But no, you would not have to "prove in criminal court that they had knowledge of the illegal transaction".
As you correctly stated earlier, ignorance of the law is not an excuse and won't get you a pass. Visa has more attorney's working for it than the govt. Visa has more internet and web connections than you or I. The information is not hidden, or secret but published right on the websites where VISA and Paypal are processing the transactions. In fact, it says on your receipt from Paypal what you purchased, right down to the number of bottles, etc.
So a federal prosecutor would NOT have to prove they have knowledge. That proof is already demonstrated by the fact the items they are processing are clearly marked by the manufacturer and clearly advertised by the Merchants selling them.
So claiming ignorance of what they were selling is just not an option for them.
IF PH's merchants were selling them and calling hiding the labels, hiding the ingredients, calling it Beef Gravy or something...then sure. They could claim ignorance.
But there is no option for that in this case. The information is provided freely by the merchants on every website where they are soled.