[rot13xor]

I'd expect Costco would require receipts for returns, even for online purchases, like most stores. Then the store would only refund the amount after discounts. But perhaps Costco is more trusting of their customers because they have to pay for membership.

[sojournerc]

I'm a member and am nearly certain they can just lookup what you've bought on the membership. They scan the member card for any purchase.