This is a model most search engines and especially directories use. For search engines like Google and Yahoo paid inclusion results are listed as advertisements above and to the side of natural organic search results. Some other search engines will spider sites more often than non-paid sites, and sometimes treat them differently; resulting in superior ranking. Previously some of the popular directories like Yahoo! charged e-commerce sites around £150 for a listing, and currently the vast majority of directories (except Dmoz, Joe Ant and a few others) charge for an express or favourable top page listing.

Below is an example of where the paid inclusion results appear for the Google search engine,