From your judgment, and experience towing trailers, would you say that guy knows his limitations?
Hard to say, they are still pictures. He may be taking it down his driveway at 5 mph, I'm not willing to speculate like others.
How to do you propose to handle the people that don't know, or care, about limitations?
Hmm. Maybe they could give real driving tests to get a drivers license. Your license could have validations for how fast you're allowed to drive, whether you have the sence to haul a heavy load, etc. The last 2 numbers on your license plate could indicate your speed limit, the first letter could indicate whether you are allowed to haul anything.