I think the problem with your last point is that while you, as a CTO whose job it is to know this, know the market salary, the person you're hiring probably does not. Like, I am more experienced than the OP, and my sense of what market salaries are in different places for different skillsets is incredibly hazy. So in light of this, it probably makes more sense for a candidate to, as a rule, push back even without specific knowledge of "$50,000 would be a fair salary" (to use your example), in case it's true. It would be a lot easier of course if there were more salary transparency, but employers don't want that.