Chinese police have, however, proven unable to effectively police higher tier prostitution practices. The nature of concubinage and second wife practices makes it more suited as a target of social action campaigns rather than conventional police action. Because of social changes, for example, Chinese police are now professionally constrained not to intrude on people's personal relationships in an overt or coercive manner. Police forces around China also differ as to how they approach the subject. In some areas, "massage parlours" on main streets are known full well to be brothels, but are generally left to function without hindrance, barring occasional raids.