I basically broke out all of my recent job considerations from my headhunter contact (used the high end ofc). 4 in total. I landed an offer right in the middle of those 4. So possibly just a tad above my market value. My counteroffer was on the very top end, 50% raise. They met me at 45+%. The plant manager fully backing me against corporate helped a lot. Relationships with folks near the top, though not at the top, that know your value and can speak to it are important. Corporate ONLY wants to look at % raises. They're obsessed with that metric and think folks will just be happy with a promotion and a few extra bucks, no thought of the labor market at all...sad. Hell, my boss wasn't even in the conversation at all. I've learned to be sure to have someone on your side that will be a major part of the internal discussions.
My "worth" is possibly tougher to quantify and prove out if we're being honest, without a lot of work proving out numbers, so the market is a nice shortcut and objectively verifiable, so that's what I relied upon in short order. It's also what they would HAVE to pay if they rejected my counter outright and I walked (I would have turned in my 2 week immediately and this was communicated, in respectful terms). I mean, if the company expresses how little they value you, not just now, but in future negotiations, there's no reason to stick around at that point. So I was fully ready to walk and made it known.