Escorts and escort agencies have historically advertised through classified ads, yellow pages advertising, or word-of-mouth, but in more recent years, much of the advertising and soliciting of indoor prostitution has shifted to internet sites. Sites may represent individual escorts, agencies, or may run ads for many escorts. There are also a number of sites in which customers can discuss and post reviews of the sexual services offered by prostitutes and other sex workers. Many sites allow potential buyers to search for sex workers by physical characteristics and types of services offered.