Why do hairdressers just do what they like with your hair ?

Why do hairdressers just do what they like with your hair in spite of what you ask for. My wife went at the weekend to have her long hair cut as she had been growing it again but as it was getting sick of it in this summer heat. She specifically asked the stylist for a short straight bob with no layers and no choppy bits. So what did she end up with ? A short choppy bob with at least 2 layers at the back ! I asked what she said to the stylist when she saw the finished result and although she was not pleased all she said was "well what could I say after it was cut ?" What should she do, how do you get a stylist to actually stick to what you ask for and what recourse do you have if they don't do it as you asked ?