It's like buying milk. I couldn't tell you exactly how much I could buy a gallon of milk for right now (without looking it up). But I could tell you that it is for around five or six dollars. I could also tell you that organic milk is a bit more and the store brand is a bit less. I could also tell you it is likely to be a bit more in a small, boutique store than a large chain store and cost a bit more in the middle of NYC or SF than it would cost in the outskirts of St. Louis.
In short, I know enough about the cost of milk that if it is priced at $16 a gallon or $1.50 a gallon that it is unusual and, despite not knowing the exact 'normal' cost of a gallon of milk, that I can assume I can walk away and get some somewhere else in the market for a 'normal' price.
I think most people are in my shoes when it comes to milk and I think most employers in tech have a pretty good idea what a normal salary for a position is, especially those who have written checks for those positions for a while.
If you are finding that is not the case, I would wonder why.
The "10X developer" may be a bit of overhyped mythology, but underneath it is the very real idea that developers vary enormously in their abilities and the amount of value they can add. While the variance in their salaries doesn't capture the variance in their productivity, perhaps, there are many situations where there is profound business sense in paying one developer 2-3x more than another.
The problems are: (1) Everyone thinks they're that 2-3x guy; (2) office politics would sooner or later lead to the news getting out and a profound sense of injustice spreading like a wildfire.
I've had employers think that $80k was a reasonable offer for me (when I was making $200k).
