Not all pet foods are alike, neither are the companies who make them. I feed my guys Eagle Pack and Wellness foods, which are manufactured in the United States, have very high meat protein content (read the label) and have been in business a long time.
Dogs and cats do not need grains in their foods - they are carnivores. Look on the label for meat content - if the first three or four ingredients are not meat (beef, chicken, turkey or a type of fish) but rather a meat by-product or a grain, the quality is lower and you should pass on it.
Also, check the internet and read about the company that makes the dog food (will you ever be surprised!). It makes sense that companies that make products other than pet food (Menu Foods, Effem Foods, Quaker, etc.) are not in the pet food business and consequently, their standards are not the same.
Like people, the better quality of food you eat, the healthier your dog will be. Both Wellness and Eagle Pack Pet foods use only human grade meats and ingredients, and that means alot to me, since I don't want my babies eating the animal equivalent of McDonalds every day. I've attached a link to their websites in the sources.
When it comes to your dog, it really does make a difference if you pay a little more attention to the ingredients list on the type of food and treats you buy. Take the time, weigh the cost and you and your dog will be the better for it.