Exactly this. There's a reason using past salary history in employment is illegal in California.
Though you should know that doesn’t stop interviewers from asking.
Oh, I'm aware. I've had interviewers ask me questions that would make a lawyer wince if they overheard. It being a law should provide some incentives to not do illegal things, even if they are rarely enforced.
It's a b2b co., this is how they appeal to their clients. This is their product.