Non Smoking rooms

What is your policy with people who smoke in non smoking rooms although they are clearly indicated as non smoking rooms. It is a most disturbing phenomenon because we also have the alternative of smoking rooms, the clients just have to ask for it. The next client who enters the room and who is a non smoker will notice the odor and complain even if the room is extensively cleaned (carpet etc) and aired. We even have a special machine to take the odor out of the room.
My colleague has been to a hotel right now where they advise the clients that they will be charged a € 60,- fee if this happens. What is your opinion?