If hiring someone to do our SEO, How do we evaluate their effort and progress?

I had a bad experience hiring an SEO specialist before, so I’ve been working on improving my approach. Hiring an SEO expert can be a great investment, but how do you actually measure their impact? Is it just about rankings and traffic, or should the real focus be on conversions and revenue? SEO is a long-term game, and results aren’t always instant. What key metrics or strategies do you use to track their performance and ensure they’re delivering real value? Would love to hear how you evaluate SEO efforts!