They also specialize in conceptualizing things, so wise decisions can be taken for the branding strategy. Most SEO specialist is able to assess the risks and know what could be the outcomes of the changes or new suggestions that they give.
While you shortlist candidates, you should check their case studies, understand the description of their work and its outcomes. You could also ask for some sort of references and details of the previous clients to understand their strategies and work outcomes. This will give you a unique point to understand.