SEO is not an appropriate strategy for every website, and other Internet marketing strategies can be more effective like paid advertising through pay per click (PPC) campaigns, depending on the site operator's goals. Search engine marketing (SEM), is practice of designing, running, and optimizing search engine ad campaigns.Its difference from SEO is most simply depicted as the difference between paid and unpaid priority ranking in search results. Its purpose regards prominence more so than relevance; website developers should regard SEM with the utmost importance with consideration to PageRank visibility as most navigate to the primary listings of their search. A successful Internet marketing campaign may also depend upon building high quality web pages to engage and persuade, setting up analytics programs to enable site owners to measure results, and improving a site's conversion rate.In November 2015, Google released a full 160 page version of its Search Quality Rating Guidelines to the public,which now shows a shift in their focus towards "usefulness" and mobile search.
SEO may generate an adequate return on investment. However, search engines are not paid for organic search traffic, their algorithms change, and there are no guarantees of continued referrals. Due to this lack of guarantees and certainty, a business that relies heavily on search engine traffic can suffer major losses if the search engines stop sending visitors.Search engines can change their algorithms, impacting a website's placement, possibly resulting in a serious loss of traffic. According to Google's CEO, Eric Schmidt, in 2010, Google made over 500 algorithm changes – almost 1.5 per day.It is considered wise business practice for website operators to liberate themselves from dependence on search engine traffic.
In addition to accessibility in terms of web crawlers (addressed above), user web accessibility has become increasingly important for SEO.
Optimization techniques are highly tuned to the dominant search engines in the target market. The search engines' market shares vary from market to market, as does competition. In 2003, Danny Sullivan stated that Google represented about 75% of all searches.In markets outside the United States, Google's share is often larger, and Google remains the dominant search engine worldwide as of 2007.As of 2006, Google had an 85–90% market share in Germany. While there were hundreds of SEO firms in the US at that time, there were only about five in Germany. As of June 2008, the marketshare of Google in the UK was close to 90% according to Hitwise.That market share is achieved in a number of countries.
As of 2009, there are only a few large markets where Google is not the leading search engine. In most cases, when Google is not leading in a given market, it is lagging behind a local player. The most notable example markets are China, Japan, South Korea, Russia and the Czech Republic where respectively Baidu, Yahoo! Japan, Naver, Yandex and Seznam are market leaders.
Successful search optimization for international markets may require professional translation of web pages, registration of a domain name with a top level domain in the target market, and web hosting that provides a local IP address. Otherwise, the fundamental elements of search optimization are essentially the same, regardless of language.