There are thousands of ninth and tenth graders in need of geometry tutoring services in Chicago. Of the twenty or so companies in town currently offering geometry tutoring, parents of high schoolers view the quality of each individual tutoring service to be about the same.
There are thousands of car dealerships that serve millions of consumers each year. The dealerships vary by location, offerings, and quality, allowing consumers with an array of preferences to find vehicles that match their individual needs.
A few major airline companies represent a great majority of total air travel. Consumers consider all different flights to be essentially the same, and comparison shop for the lowest price.
The government has granted the U.S. Postal Service the exclusive right to deliver mail.