The search engine then checks other keywords on subsequent pages and also sees how many other websites are linked to the page in question, to determine the site's popularity. According to AltaVista employees, around 25 per cent of websites are filtered out at this first stage because they fail to comply with requirements. Inclusion is normally free of charge, although companies can now pay a fee to ensure that their website is at least read by an editor - but this does not guarantee inclusion. They examine how these keywords are interlinked and general plausibility is also established. This material is analysed and, together, provides the data for the ranking.
Implausibility is a sufficient reason for exclusion and being placed on a blacklist.
But a placement on a leading search engine is not necessarily definitive, since engines make repeat verifications to test websites and may take them off their directory at any time. It is unwise, particularly with directory services that work predominantly with editors, for a site to rely on programmed replacement software - which continually updates the site, sometimes just for the sake of it. Unlike automated search engines, which assume that a regularly updated site is a good thing, editors will examine the actual content of these updates. Spamming and unsuitable keywords will see you on the blacklist. Certain providers offer search engine placements for sale, often through auction, and calculate fees on the basis of click rate.