I also agree that it is important to buy a good quality dog food for your dog. Just because it is expensive does not mean that it is necessarily better, and veterinarians are paid to sponsor certain dog foods, like Iams. They provide benefits for the vets who are learning about veterinary medicine in college, and then when they start their own practice, they also feature Iam's dog food.
Some dogs are much more sensitive to what they eat then other dogs are, and can seem to do all right with even the cheaper brands, but they would still be better off with a higher quality of dog food. It is kind of like it is with people. Some people seem to eat mostly junk food and still are fine, others need that high quality diet to bee healthy.
One very important thing with dog food is to check the ingredients, and look for added healthy foods and vitamins, like flax seed, beet pulp, and other nourishing supplements; and avoid any food that lists corn as a main ingredient.
