Regardless of whether you are hiring an SEO consultant or an SEO company, you need to do your research and make sure you are hiring an actual SEO expert. Not someone who went to one SEO training workshop or a weekend conference and now claim to be a so-called expert.
Let me say this... I have personally run (on average) about 50 recurring SEO campaigns per month, each and every month, for almost 10 years now. Every niche you name it, the toughest keywords, the biggest Fortune 500 brands all the way to local dentists, lawyers, plumbers, contractors and even e-commerce sites all across Canada and the US. On top of that, literally optimizing hundreds of websites not to mention my own personal network of sites/blogs that I still run to this day.
You will be hard pressed to find any freelance SEO expert in North America with as much hands on SEO and link building experience. The best part? You get the agency experience without the agency price tag from one of the hardest working and most respected SEO experts around.