Understand that only text gets indexed. Search engines do not index graphical text or text contained in images. Frequently web designers only put the name of their site in a company logo or image at the top of the page. This is one reason it is often difficult to find corporate home pages. If you encounter this problem, try searching for one of the company's specific product names rather than for the company name.
Indexing is neither comprehensive nor objective.
Not all search engines index complete web sites, instead indexing only a certain number of words per site or a certain number of pages. Some web authors include commands that prevent search engines from indexing part or all of their sites. Sites may change considerably between indexings so search engines often produce references to sites that have changed or no longer exist. Some web authors manipulate search engines by deliberately providing inaccurate information as to the site's content. As for-profit businesses, some search engines give preference to their advertisers' and business partners' web pages, usually without disclosing that they do so.