I don't even really understand why that plan would be "enraging" or really even counter to what customers expect from Costco. Assuming you continue to buy from Costco, and most Costco customers are regular buyers, you'll effectively get the money back in future lower prices and end up paying the same total amount on Costco purchases as if they had sent you a refund check.

I can see the appeal of an immediate refund check, but using the tariff refund to lower future prices for customers in a way that drives continued sales seems like both responsible thing to do from a fiduciary perspective and a not unreasonable compromise for the customer. Many companies would, and will, simply pocket the refund.