There are people who will not only not purchase your home, they may not even view it if it has the smell of cigarette smoke. I have shown up at a home with clients who can smell smoke before they even enter the home and turn around and walk away.
It is difficult to get rid of the smell of smoke without removing carpets, washings down cupboards and repainting the walls. Some smokers have realized this and are starting to smoke inside the garage. Unfortunately the smell is still offensive and the smoke seems to still linger in the home.