Does SEO work? Could you suggest good SEO companies?

Like most other web professions, there's a huge variance in quality. We've interviewed many applicants for dev spots that have tons of experience in javascript but can't really describe what this means. Likewise I believe there are a ton a BS "SEO Experts" who watched a view videos vs some who have really taken the time and spent years learning how everything "works" and applying that to your business goals in a way that's both ethical and effective. I found many cool specialists on UpWork