Originally Posted by
apados
Costco used to be Discover only, but they signed a deal a few years back to exclusively accept AMEX in stores. In their online store, they can accept other cards, but in-store credit card purchases are restricted to AMEX cards. Debit cards can be used ( I believe as mentioned above for non-signature i.e. pin transactions).
I don't recall what the exact agreement was, but i'm guessing it resulted in a discounted merchant fee for each transaction etc. along with the costco branded amex card etc.
When was Costco only Discover? I don't recall that being the case.
You sure you're not confusing this with Sam's Club? Sam's was Discover-only until a couple of years ago, when they started accepting MasterCard as well.
I didn't get my own Costco membership until 2002, after they went Amex-only, but growing up in a family that shopped Costco heavily, I never recall anyone in the family having to use a Discover card at Costco (though they mostly wrote checks).