I once asked an NYC cop friend if someone has to identify themselves as a cop if a hooker asks them if they are law enforcement.  He laughed.  He said that cops lie all of the time to bust perps of all kinds.  These ho's are fooling themselves with this disclaimer.  With that said, my friend told me that actually busting someone for prostitution is extremely hard because you have to catch them in the act of actually bargaining money for sex.  That's why ho's can post obvious advertisements for sex without getting busted.  That's also why LE has cracked down on massage parlor licenses.