Finance and Business How do gift cards from Costco work? How do gift cards from Costco work? To get into a warehouse, simply flash one of the gift cards to the person at the door. Then pay for your purchase with the card. Costco's policy lets you cover any remaining balance with cash or a debit card (no credit cards allowed).Mar 19, 2021 Related Posts:The complete list of Comenity Bank credit cards can be found on the official Login page.Can I convert a gift card to cash?Does CardCash pay instantly?Can you buy trivago vouchers?