Google's search algorithm is estimated to have 500-600 changes made annually. That is over one per day on average! If your SEO provider is not keeping current, the likelihood of your ranking high over the long-term is not probable.
In the end, search engines are interested in providing the best results to their users. This means that effective SEO should be taking the same approach by providing optimal content and design. Ultimately, this is what will help get better search engine ranking.