I agree. The system is far from perfect. We have laws that only a lawyer can read and exceptions to the exceptions written into the laws. This allows both sides to find that one word in the rules to make it read their way; at least in their minds.
Then we have cops that are TAUGHT when in question write the ticket; arrest them; and let the courts figure it out. This applies to all police work not just DOT or traffic. Problem with DOT tickets is the court is often miles away so it is easier to just pay the fine.
The biggest loop hole I see on this forum is I am not Commercial OR it is a hobby.
You can blame that loop hole on big boats and RV's. It is those guys that got it written into the law. Life would be a lot simpler if the feds would just say anything over this size these rules apply.
With that said you are dead wrong on your point of view.
You even said this was a farm tractor. A farm is commercial. Yes you may only farm on the weekend; you might even loose money at it; but it is still a business.
Yes he would be classified as a private carrier so for hire carrier rules would not apply.
But since he was out of state; log book; federal truck inspection; DOT #; medical card; fuel permit; apportion tags; all sound like good charges. Then we add no permit for oversized; no oversized signs; and most likely over weight and I would say he got off easy.
From the info you have given I would say your friend is SOL. He just as soon pay the fines and be done with it.
As far as being over weight.....
Yes I do not know the exact truck engine; cab; or axle ration so there is a chance he was not over. That is why I say most likely; because there is a very good chance he was over if not very close to being over with a tractor of this size.