You might want to rethink your example if the counterparty offers you 50% more than you wanted then you reject the deal; it makes adding the framing a bit pointless because it is clear you weren't ever going to accept the job for $200k.

And you're underestimating how much of an impact the broader market is having on Meta's thinking in this scenario. If your silver tongue or secret number was a factor here then everyone would end up being overpaid because they wouldn't reveal that they were happy to work for a reasonable amount. It doesn't matter how much or little Meta knows, they're only going to offer $300k if they have a reasonable belief that you can find a job for $300k somewhere else; informed by a pretty detailed analysis of the employment market. And in fact that appears to be exactly what happened in your story. Nothing about that dynamic has anything to do with your salary history or spending habits and them getting better information on those things doesn't change your negotiating position. Since a key factor is the future, even if they know you'd say yes to $200k, they'd still be best served offering you more money. I've had that happen to me 2 or 3 times because I'm a sloppy negotiator and don't try very hard to optimise salary.

> You might want to rethink your example if the counterparty offers you 50% more than you wanted then you reject the deal

I rejected the deal because I got even more elsewhere. My framing still stands. In a case when only one employer has the information, sure they’re better served by offering me more money. But in an environment where all of them have the information, this no longer is a problem. At a system level, this is a problem for employees.