There are two primary schools of thought when it comes to SEO. The first is white hat SEO, in which the SEO Specialist, agency, consultant, etc. carries out SEO activities that are deemed appropriate in the eyes of the search engines. The second is black hat SEO. This involves using tactics that aren’t approved by the search engines in order to attempt to gain a quick improvement in rank and SERP (search engine results page) presence. The search engines continue to get more sophisticated as time goes on and Google has been making some huge tweaks to the algorithm in the last few years (Panda, Penguin).