Matt cutts google, the basics
SEO expertise includes knowledge of search engine s and their vulnerabilities including styles for recognizing keywords. The Seo firms have the requisite knowledge base to analyze web structure, data mining methodologies and ways and means to get their clients pages ranked high on the 'hit' list. Getting a search engine to pick up the relevant phrases from an article help to gain a high ranking list in the search result. The mediocre SEO firms are typically short lived. In face, there are very few good firms.