We compared the annual incidence rates of arrest for patronizing a prostitute for two groups of clients of prostitute women identified in Colorado Springs, Colorado, between 1970 and 2000. One group included clients first detected through arrest by the police; the other included clients first detected through public health activities and research. If the two groups were otherwise comparable, a lower arrest rate for clients first identified through arrest would imply that arrest has a specific deterrent effect on patronizing. We obtained the data on these two groups when the second and third authors directed the sexually transmitted disease control program of the local health department. The Colorado Springs police provided data on clients arrested for patronizing. Arrests constitute direct evidence of patronizing. Therefore, by using arrest data, we avoided the well-established problem of clients underreporting their patronizing activity in surveys [16]–[22].
http://plosone.org/article/info:doi/10.1371/journal.pone.0000060#article1.body1.sec2.p1

Perhaps prostitution could be stopped if the crimes of prostitution or being the "John" weren't treated as typical misdemeanor crime. Pay a fine...go back to what you were doing. It seems funny to me that so many crimes are easily "paid off" at the local city hall.