Some search engines use algorithms to determine and weed out low value sites, helping you find the most genuine information out there based on your search terms, while others rely on the popularity of a page to determine how it ranks against your search terms. Popularity, though, doesn't necessarily mean something's factual; it could just be a well-told tale.
Not all search engine results are created equal, either. There are also paid advertisements that sit above the organic search results the search engine finds based on your search terms. Google, for example, places relevant paid ads above relevant organic search results, and a subtle background color change may be the only thing that catches your attention to indicate any difference between what is paid content and what is not. There is normally a line of text that states that the results are ads, but on a page full of text-based results, that's easy to overlook. A fraudulent or ill-informed Web site can just as easily bid into ad positions and work its way into top search results just as genuine Web sites do, making it difficult to know for sure if the number one site in a search result listing is bogus or not.