Love Costco. Better quality products, IMO, than Sam's Club at the same (and sometimes lesser) prices.
Their return policy is generous, too generous perhaps. Yesterday, I purchased 21 (24 count) packages of chocolate chip cookies to be sold at a homecoming "tailgating" party. We sold about 10 or 11 of those. One person suggested I just "take the rest back." Now, there is no doubt I could have done that and they would have cheerfully refunded my money. But, I refused to do so. That's just wrong. It's not their fault that I bought too many (and I bought the amount suggested by the people organizing the fundraiser), and it just felt wrong to take those cookies back when I KNEW they would have to be destroyed by Costco (since they are not a "sealed" package, but only a blister pack.).
I've seen people returning 1/2 eaten trays of food, etc, and to me, not something I would do. It takes advantage of their generous return policy and drives up costs for all shoppers.
I have returned things that were broken, spoiled when opened, or didn't fit properly, and never had an issue. The fit thing, in particular, is fair game IMO because they do not offer changing rooms so there is no way to "try before you buy."