Keyword research is crucial to any content marketing (or SEO) campaigns. The idea is to offer a comprehensive keyword research along with competitor analysis.
If you are a “niche expert” who have specialized knowledge in few topics then you can do better topic research than anyone else. And you can make your gig unique by providing related services.
For instance, I do not know how many times have I edited the titles and subheadings of this blog post as I was not sure whether to create two separate blog posts for the “review” and “ideas” or to publish it as a single blog post.
So you can provide competitor research or even provide a full blog post outline with a search friendly title and subheadings as an add-on or as another gig.