personally I'm not worried about what the client thinks. I don't smoke while work in the first place but if I ever did go back to smoking cigs or hired an employee who smoked there would be only 2 rules.
don't throw your butts on the clients property and you can only smoke at the truck/trailer after your work is done or if your taking a break.
besides that I'm not into hiding what I do just because someone might find it unacceptable. if someone doesn't hire me or want me working on there property because I'm a smoker then I don't want or need them as a client.