Here are three possible reasons to hire an SEO consultant or digital marketing firm to help your company with SEO:

1) You are committed to a content marketing strategy and want to ensure you get the most leverage, in terms of organic search traffic, from the content you are going to produce. 

2) You already have a large amount of content on your website, but you don't have visibility (rankings) in Google search results for keywords that are important for your industry. 

3) You are planning a website redesign or replatforming and want to ensure that you don't lose rankings in the process.