Pets have accidents, many of which you don't notice until they've become set-in. These stains can affect your carpet and flooring, drywall and trim, and your furniture. It's important to address them before you list your house because buyers will notice -- and perhaps smell -- the stains immediately. If there are stains in your carpet, a simple spot treatment will rarely do the trick. It's best to replace stained areas with new patches of carpet and, if necessary, carpet pad. Stains on laminate or vinyl floors should be replaced, as well.
If you have stains on your walls or trim, it's ideal to replace those, too. If that's not in your budget, you can try the very best odor-free primer you can find. A good primer should properly seal the stain -- and the pet odor -- and neither should return.