The answer to 'upholstery smells bad' is that there are several common causes, including spills, pet odors, mold/mildew, and general dirt and grime buildup. Symptoms may include a persistent, unpleasant odor that doesn't go away with basic cleaning. Solutions depend on the root cause, but can involve deep cleaning, deodorizing, and in some cases professional upholstery cleaning.
If the smell is mild, you may be able to address it with DIY methods like spot cleaning, using a fabric deodorizer, or steam cleaning. However, for more stubborn odors or if the upholstery is heavily soiled, it's best to hire a professional upholstery cleaning service. They have the right equipment and expertise to thoroughly clean and deodorize your furniture.