Law enforcement agencies often use -- and courts usually allow -- "sting" operations, where officers go undercover to catch people involved in the sex trade.
Sting operations are a practical response to the way prostitution is carried out. Most other crimes come to the attention of law enforcement through victim or witness reports. Prostitution, however, presents unique enforcement challenges. Most prostitution is consensual, in that the parties to the encounter agree to an exchange of sex for money. It's in neither party's interest to report the other. And because these sex acts usually occur in private, the chances of innocent third parties observing and reporting them are slim. As a result, police agencies mainly enforce prostitution laws through sting operations.
Studies have found that women account for the vast majority of prostitution arrests. This finding is due partially to the prevalence of women as sex workers, but some suggest that police practices contribute to the disproportionate arrest rate. For example, police agencies historically used male decoys posing as potential patrons much more often than female decoys posing as prostitutes.
Critics of sting operations allege that law enforcement agencies employ them disproportionately against women, especially "streetwalkers," who are often poor minorities and immigrants. These critics also argue that the police do not target prostitution customers, colloquially known as "johns," nearly as much as they do sex workers. Regardless, courts throughout the country have routinely rejected challenges to prostitution stings, including when the challengers have argued that these practices discriminate against women. In fact, police officers are not only allowed to conduct sting operations—they are afforded considerable discretion in executing them.
Knowing that police officers go undercover to catch them, sex workers often ask potential "clients" to engage in some degree of sexual contact, which the workers think will prove that they are not undercover officers (workers are counting on an officer's refusal). Accordingly, officers argue that effective policing sometimes requires that they participate in limited sexual contact to convince sex workers that they are not police. Although courts have consistently allowed sexual contact in this context, there are limits to what they will accept.
In a 2009 Minnesota case, the appellate court reversed a sex worker's prostitution conviction on the grounds that the investigating officer's behavior was so outrageous that it violated her due process rights. (State v. Burkland, 775 N.W.2d 372 (Minn. App. 2009).) While discussing the possibility of purchasing sexual services from the defendant, the officer initiated and escalated sexual contact by fondling the defendant's breasts. The court distinguished this conduct from acceptable undercover behavior because it did not occur in response to a demand by the defendant and was unnecessary to the investigation.
In another 2009 case, this one in Pennsylvania, the police employed—quite literally—a citizen to accumulate evidence of sexual impropriety at a health spa. (Commonwealth v. Sun Cha Chon 983 A.2d 784 (Pa. Super. Ct. 2009).) State police paid him to purchase sex acts from female spa workers. The court dismissed the criminal charges, again on a finding of outrageous government conduct. The court found law enforcement's conduct "shocking" and "outrageous." However, it did not rest its decision exclusively on the fact that the police paid an informant to have sex with prostitutes; it also cited the informant's questionable motives and the officers' unprofessional conduct, which included joking about the sexual encounters.
These cases help define the limits of what courts consider acceptable enforcement methods. But, police agencies still have considerable leeway when investigating prostitution rings.