When selling a home, there are issues that can be deal killers. One of them is smoke from cigarettes or cigars. Smokers can't smell what non-smokers do. Buyers will immediately reject a house if there's such an odor, even if it is their dream house. Oftentimes they will do an about face at an open house if they smell it at all. I saw it happen recently at a million dollar property!
Even if you only smoke outside on the patio, it gets in your clothes, carpet, and furnishings. If you are listing your home, ask a non-smoker to tell you if they can smell it.
Given that most people don't smoke, you will be severely limiting buyer prospects for your home so it's critical that you do what you can to eliminate it prior to listing. Be prepared. It's a lot of work and can be costly if you have to paint but failure to do it is real estate suicide.
Here are some suggestions from Peter Hotton, Handyman on Call for the Boston Globe.
The basics are to clean, and clean again, then wash and wash again. First, remove any wallpaper. Then wash the walls to remove any paste. If the paste is difficult to remove, let it dry, then sand and re-wash. If the odor pentrated old wallpaper to the exposed walls, the walls must be washed.
Wash everything: walls, woodwork, floors, and ceilings. Any detergent will work but trisodium phosphate (TSP) is better in many cases and so is any citrus cleaner such as Citrus Green. For floors, a wet Swiffer is good. Clean all rugs, plus upholstered and wood furniture. Regular use of Fabreze can help but it really only masks odors for a short time. I've heard that Room Shocker, placed in a closed room for 12 hours will do wonders. On the net at Biocidesystems.com.
After washing, repaint the walls and ceilings with a flat latex wall paint and ceiling paint. Paint woodwork with a latex primer and TWO coats of an eggshell latex paint.