Some search engines read other companies databases. That is especially true with metasearch engines. Depending on the timing of the submission, the database owner and the schedule and activity of the robot, it can take anywhere from seconds to several weeks to get listed in an index. Rankings are based on actual search activity of millions of Internet users. New sites submitted or found during a crawl are listed in the search engine and given an opportunity to be found by searchers.
Most engines weight favorably sites that users visit and spend time at for particular search topics.
They are then ranked higher than sites that are consistently ignored. Most robots follow legitimacy guidelines they establish themselves. That includes the number of times a word shows up on a page, subliminal suggestions and other sneaky tactics. Generally rankings are based on key words. Some engine search results are based solely on comparing the user's search query to the content of millions of Web pages.