Am I held accountable if a customer smokes in my restaurant after I have prohibited smoking?

Smoking and displaying oneself immodestly (tabarruj) are grave Munkarat (reprehensible acts) that must be condemned, and it is forbidden to assist in them. You bear no sin for what customers do as long as you do not provide them with cigarettes and shisha, do not permit unlawful mixing (ikhtilat), and do not create an atmosphere conducive to it through music and objectionable television series. You should condemn these acts to them gently and wisely, verbally and in writing. A separate place should be designated for women and families to avoid unlawful mixing.