It's true and it's too bad. People (customers) **** enough as it is, but honestly, they have the right to ask. However, most can be discrete. Many of the trades in CA are mandated to display their license number on their truck. Not all, and some that don't have to do it anyway. That way the customer can look you up on the state website.
I carried a license for 40 years and was never asked except at supply houses and building depts. Never by a customer. However, my estimate sheet holder had my info plastered on the inside so if I got that out it was easy for anyone to see. Could have all been phony and the bonding company's card had my number in the largest size, so I just put that one on top. The real license looked more like a driver's license and hard to read. Never had a card that showed ins info. No one asked.
I retired my license because of this. If I wanted to work under contract I wouldn't hesitate. It wouldn't mean anything but the contracts over the years didn't mean a lot. In fact, I used a proposal and contract as the quote, or
estimate, as it is mislabeled. They sign that and we're off to the races. In my door and window business I took a deposit. For repairs and alterations, never.
Oh, and my proposals had the entire required spiel cut and pasted from the CA contractors website and printed on the back. This spells the laws out for the customer. Hardly did they ever flip it over to read. The overwhelming average of contracts that I saw by others had none of this info.