There is no doubt that you need a good SEO firm for your webpages to do well within search engines which is where all the traffic lies and which is where all the money that you expect to be making from your efforts would be coming from. However, there are quite a few different SEO service providers all trying to impress clients with their work, however only a few of them tend to know exactly what it takes to get higher rankings for different keywords on various search engines.
What you need therefore is not just any SEO firm, but the right SEO firm that would only help your website rank for better keywords instead of tarnishing your online reputation. You really need to have a system in place to plan what keywords you would like to be ranking for. You cannot simply hire an SEO firm and ask them to help you rank your website without first knowing what keywords you would like to be ranking for and how difficult it would be to rank for them.
Every keyword is viewed differently by search engines which is why you need to be starting your SEO with an appropriate level of keyword research. So, the best way would be to have an se ranking tool after hiring an SEO firm so you can check if your keyword rankings are improving on search engines.