An SEO expert can analyze and decide effective keywords to promote your website. He can provide you expert ides in different aspects like on page optimization, link building, off page optimization, keyword analysis, visitors’ analysis. It is certain that they understand better to provide you enough guidance on how to improve your search engine rankings.

Yes, but beware of those that use Black Hat methods to quickly improve your rank and get paid. In the long run you can be banned from the search engines.