Not only gross, but doesn’t Costco track how many and the timing of customers returns? I’ve heard rumors over the years those with excessive returns may be denied membership renewal...is that true, oh Costco Guru?
The short answer is Yes. The longer answer is that there are too many people, and too many refunds, for them to keep up with everyone in the moment. The clerk who handles the refund is given HUGE leeway on whether to accept the item. In most cases, they'll take back the item without blinking. If it's something like a ten year old mattress, it's going to take a bit more research into it.
The reason they scan your membership card at the Refund Desk is so they can pull up your shopping history. They can see the item you're returning, when you bought it, (IF you bought it), what you paid for it, any adjustments to that price, and then (very important!) any NOTES on your account. If you are a habitual refunder, not for one-off items, but repeated returns on the same thing, or abusive toward the generous refund policy, or just a pain in the rear problem member, there will likely be notes in the account that alert the refund clerk to beware. If things are severe or abusive enough, the clerk may call for a Manager to come to the desk and review things for them. If the Manager signs off on it, the refund goes ahead. If the Manager agrees this is a refund that shouldn't happen, the Manager tells the member why the refund won't be allowed.
The Refund Clerk will then make notes about that situation on the account, in case the (disgruntled) member tries to return the item at another warehouse. It happens all the time. In those cases of members who flat out abuse the refund system, and it happens often enough, or for a reason that the membership isn't worth maintaining, the member may have their membership cancelled, or not allowed for renewal. But those cases are pretty rare.
Most members at Costco are honorable, cooperative folks who appreciate the value they get for their dollars spent. It's the abusers, those "too smart for their own good" types, and outright cheats who are usually caught, and receive appropriate results.
Bottom line: Use your common sense, and don't be a jerk. Abusive returns affect the entire membership community. If you have a ten year old mattress, don't return it and act all innocent like it's no big deal. You KNOW what you're doing. And you should be ashamed of yourself.
Dave