Yes, the SAT prep industry is nearly entirely fraudulent. People will pay you for something they want, regardless of whether you can actually give it to them.
Perhaps to the degree that it presents expensive in person classes as a much superior alternative to using a test prep book for motivated people.
This is an extensively studied question. The effect of preparation on score is negligible whenever anyone tries to measure it.
I have noticed that people generally really hate the idea that test prep for the SAT does not really work. (parent was downvoted) I’m not entirely sure why that is.