Technically, there is a difference in CA based on the truck GVWR weight which makes the salesman correct (hard to believe isn't it?).
CA laws have not kept up with technology. A "Pickup" is defined as having an open bed, where the truck itself weighs less than 8K and the GVWR is below 11.5K. I would contend none of the big three trucks weigh less than 8K. And a F350/3500 dually is way over the GVWR. So those vehicles supposedly should stop at all the weigh station.
The truth is yu don't have to stop, even with a MDT or HDT, if it is a private tow vehicle and towing an RV. Similarly, what we call pickups are also exempt if towing an RV. According to the law you must stop if you are not towing an RV with your pickup. But if you do, the weigh master, along with a line of real truckers, will blow a gasket. They don't have time to deal with the hundreds of thousand pickups going past each day.
As long as you don't have commercial signage all over the outside of the truck, you are fine not stopping when not towing.
Now CA did introduce new weight stickers which you are supposed to buy when your GVWR is over 11.5K. It is strictly a revenue generating idea. Once again enforcement on F350/3500/F450 (duallys) etc. vehicles is nil.
The important thing is to buy the truck you need and don't fret the bureaucratic B.S.
