From what you are writing about it seems that the message that you received from upper management is that you are not to turn away any guests if you "believe" that they may engage in criminal acts.Under the law, the possibility that the guests may engage in a criminal act is not a basis to refuse service to him or her. If the guest is actually engaging in criminal conduct your hotel can legally ask the guest to leave. However, to prove prostitution, one usually has to pretend to be a "john" and be wired to record evidence of prostitution as part of a police sting.