Also remember that 99.9% of the time the local store does NOT breed, incubate, hatch, or raise their chams, so they have no idea what incorrect supplementation does to them. They don't hold their stock very long either. If they actually had these animals long term they would soon find out just how bad the husbandry information they spout is. They MIGHT be getting this information out of outdated "care" books, or repeating very old outdated knowledge someone else told them. They are in the business of selling, not keeping.
Once in a while I'd find a local shop (or a particular employee who took an interest) that seemed to really be concerned about the proper care of their chams, so I'd help them get the proper husbandry info if I'd noticed something was off. Once you get this sort of rapport established with a shop it can benefit everyone.
I remember working with a herp shop in CO that was interested in doing a demonstration setup for chams. I ordered a panther from a breeder, set up a screen cage in a different area of the store (most of it was too hot due to all the other "tanks" and big snake enclosures), got proper lighting, live plants, correct supplementation/insect gutloading, and simple fogging system. Printed out a husbandry guide that re-created that setup. Really fun, customers loved it, the cham did very well, and a customer ended up buying the entire setup and the cham. Did a similar thing for their leaf-tailed geckos. Then the shop was sold and got a new manager. Everything went back to the garbage situation it had been in before. Nothing I could suggest made a dent in what this fool believed. It was heartbreaking.