Typically, massage or beauty parlors that give more than just massages or haircuts are staffed with a large number of young women wearing attire that isn’t suitable for massage or haircuts.
Again, if you find yourself accidentally in a situation that you don’t want to be in, you can usually just decline whatever service is on offer and leave.
I’ve also had reports of ladies knocking on business traveler’s doors with offers of massages as well as excuses like “I’m thirsty, can I come in for a glass of water?
You might get calls in your room late in the evening from women looking for clients.
While my girlfriend and I danced, my husband and hers were approached not only by women, but also men coordinating work for their girls.
It is usually benign and a simple “no thanks” will do.
Ladies of the night typically hang around where they think clients will be (and where they have been successful at getting them). It probably doesn’t need to be said but you can probably tell if a woman is really interested in you for your personality or for something else.
We’ve been in some clubs in Shanghai where it seemed like most of the women inside were “working”.
But if it gets ugly, call the hotel management or the police.