That must be a diet problem. If you feed a low quality dog food, or otherwise poor doggy diet, there will be bad smells. The first ingredient in any dog food ought to be meat. If you feed the dog mostly corn, and it is not a breed that thrives on low-protein food, it will fart a lot.
I feed Purina Pro Plan, it is a step up from cheaper dog foods, 35 bucks for 35 pounds, but won't break the bank compared to Wellness at 48.99 for 30lbs.
Seriously though, dog farts are usually a sign of a diet problem, just like in humans.