earnings (not counting any gratuity received). Most transactions occur in cash, and optional tipping of escorts by clients in most major U.S. cities is customary but not compulsory. Credit card processing offered by larger scale agencies is often available for a service charge. 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. Internet advertising of sexual services is offered not only by specialty sites, but in many cases by more mainstream advertising sites. Craigslist for many years featured an "adult services" section of this kind. After several years of pressure from law enforcement and anti-prostitution groups, Craigslist closed this section in 2010, first for its U.S. pages, then some months later internationally. In March 2018 the personals section of Craigslist was closed down. In 2017, the "Adult" section of Backpage was closed down. Currently, internet advertising is the most important resource for anyone interested in prostitution. There are websites catering to different clientele, from upscale escorts to budget low end. Brothel prostitution With the exception of some rural counties of Nevada, brothels are illegal in the United States. Along with these legal brothels in Nevada, commercial sex also occurs. Due to the topic regarding legal prostitution, the rights of these establishments are neglected. Both participants in establishments such as brothels, are subjected to background checks, cleanliness checks, and working licenses at the government's request. Aside from this, many massage parlors, saunas, spas, and similar otherwise-legal establishments serve as fronts for prostitution, especially in larger cities. They tend to be located in cities or along major highways. Child prostitution The prostitution of children in the United States is a serious concern. More than 100,000 children are reportedly forced into prostitution in the United States every year. In 2007, a scholarly article stated an immigration issue pertaining to the difference between underage females committing this crime as citizens and non-citizens stating, "Furthermore, a 14 year old Chinese girl trafficked into