I have done some work at film sites where CHP are used for traffic control. I have asked quite a few of them about the trailer towing weight laws and how they inforce them (since I tow over the 10,000lb weight limit). Almost all of them gave me the same answer, if the truck and trailer don't look overloaded and unsafe, they don't bother the check it.
Once I was hauling hay back to my ranch. I had about 116 bales on the trailer (total weight with trailer approx. 15,000lbs - trailer rated at 14. 500lbs) and another 16 bales on the truck. Total GCW was about 24,000lbs. I stopped at a convenience store to get a drink and on the way back out to the truck I crossed a CHP officer going into the store. He asked me where I was going and I told him I was on the way back to my ranch. I asked him why he asked and he said if my answer was any different, we would have to talk more. Then he went on into the store. The CHP are very lenient with ranchers and farmers as long as they don't see a real safety problem.