If you look carefully at the before photo, you will notice two squares where we cleaned the walls with a dry sponge. The yellow color of the walls is the nicotine from years of smoking. Not only did we clean everything, but the house smells like new! The first thing homeowners think to do is seal and re-paint the walls, but that will only work if the source of the odor has been removed. The nicotine must be removed from the surface of the wall, then the walls can be sealed and repainted if necessary. Otherwise, the odor gets sealed in by the paint!