You might think you’re the customer at the supermarket, but actually supermarkets make most of their money by selling shelf space to manufacturers. They are the real customers.
You might think you’re the customer when you buy a newspaper or watch the TV, but the media make their money by delivering viewers/readers to the advertisers. The advertisers are the customers.
Who is the customer of public transport? The user, paying their fare to travel? Or given that (in this state) the private operators make the bulk of their money from government subsidies, would it be the government?
Are the customers of the health insurance companies sick people, healthy people, the hospitals/medical industry, or the government who are subsidising them?
PS. Okay this is probably painting it a little one-sided… in each case, the end consumer is an essential part of the picture.