I’m an average software engineer and I can’t remember a time where I took a job I didn’t negotiate the salary on. Companies that refused to negotiate were the last offers I’d consider and I end up not taking their offers. I was often better paid than my peers. And my professional accomplishments are far from exceptional, I’ve never worked for any companies you’d know, I have gaps in my CV.

LOL we might have applied at the same company. That's almost word for word what I've heard in the past: "Oh, sorry, we must have been unclear: the offer is not negotiable." I said NO and they said "OK, thanks for applying."