Simple enough
The not-so-simple part is the insurance (or discount) company lists several dozen health care providers in many cities who "accept their discount card", not to mention their other card which gives you discount at makeup and perfume stores. They are by the dozens.

Now suppose I am a clinic or pharmacy owner. I give 20% discount ONLY for people carrying that card. Isn't it against business wisdom to charge other people 20% more ??? Customers will run to the competition.

There is something I am not really getting there.