I'm sure, like most people, that you are aware that time, home life (especially cooking), and pets can make carpets stinky. You may not notice anymore, but anyone who comes into the house probably does. If your carpet has picked up a funky smell, you can try a commercial carpet deodorizer or you can go to the pantry and arm yourself with a box of baking soda. Sprinkle it into the carpet, leave it for a few hours, and then vacuum it up. For less money and a little extra work, you can try sprinkling grated potato all over the carpet in question. Let it stand for several hours and then vacuum. If neither of these methods works, stop trying to avoid the inevitable and call a carpet-cleaning company.