There are many ways to explain the market structure of the automotive industry.:
One of heterogeneous purchasers makes up the population and nearly homogeneous sellers. This means that everybody (the population) wants a car (because a car is not a luxury item), but everyone has different requirements (i.e.: compare a mother of 4 to a construction worker). Therefore, buyers are everyone in the population, and they are heterogeneous (different). Though, sellers are practically the similar. GM, Ford, Chrysler, Nissan, Honda, Toyota, etc all offer the similar products. Thus, they are homogeneous (similar).