In earlier days i.e. prior to year 2000 the thought of paying to have sites ranked on a search engine or incorporated in a directory was poor response , very limited companies were asking for payment. But due to increase of World Wide Web more and more search engines now required payment for listing/ranking. Many of less important search engine use PFI or PPC. Most popular engines have both.The engine that provide paid listing require that someone bid for position on ppc. Now other companies require payment costing hundreds of dollar to have them review the site. Some will require payment to index the pages. SEO strategies become even more important with paid listings.Maintaining paid rankings can be a time consuming and expensive process. Optimization is a legitimate promotion strategy