Aperiodicone is going shopping:

Costco doesn’t take manufacturer coupons and only take American Express. Odd.

Why does Costco only take American Express?

There are a few American Express Costco Cards, including the TrueEarnings Card. But why doesn’t Costco take other cards?

The reason is that American Express charges Costco particularly low interchange fees on each purchase. Because Costco is cheap (that shouldn’t be a revelation), they only choose to accept credit cards with very low rates.

Want to work around the system and use your normal credit card? Online gift cards are still there.