I've heard plenty of stories of people buying merchandise with restrictions and selling it anyway. Sometimes they get caught, sometimes not.
I know of people manually removing serial numbers so the items can't be traced back to them. I know of people setting up multiple companies, selling from one to another and providing documentation that it wasn't "them" when caught. I've seen stories of people buying undelivered shipments from carriers and selling products found.
Point is, you can't assume everything is counterfeit just because the manufacturer doesn't sell to amazon sellers.
I've been threatened in the past by a manufacturer for selling their items: in that case, I had bought some from Amazon directly when the price was lower, and some from another authorized dealer. There are a lot of manufacturers that think their rights go a lot further than they actually do.