If you have commercial plates on your truck it is not likely you would be pulled over with cargo. If you had non commercial plates on your truck and had cargo in the back you probably would be cited. The numbers and letters are arranged very differently. I am referring to California.
Years ago my dad had truck with a camper shell on the back. The truck had non commercial plates. He used the truck with camper shell for his work tools. He loaned the truck to a friend. The friend took the shell off, and had a wheel borrow in the back. He was stopped by a policeman and given a citation for using a non commercial vehicle for commercial use.
On occasion you will see a CHP pickup on the road. He is the one most likely to check your weight status. I have had that experience.