Not only should the ghostwriter you hire understand how to write your on-site pages in a way that they are optimized so that search engines can find them, he/she should be able to write in a way that keeps your visitor on the page. You want content that offers value; your pages should be interesting and compelling, offering information your visitor won't find on 100 other websites.
You want your business to be as profitable as possible. Don't make the mistake of hiring someone who cannot do the job efficiently, no matter how cheap their rates are. SEO content writing is a skill that not many people really possess; hire only the best!