I believe Costco will cancel (and refund) a membership at their own discretion. I’ve read stories online that they have cancelled memberships for clearly exploiting return policies, as well as other things like grossly mistreating warehouse employees.

Yep, exactly this. Costco is willing to eat a few people abusing the system in return for those sweet sweet membership profits, but if you start to seriously abuse the system they have zero problem kicking you out.

I saw this happen first-hand while I was waiting in line to renew my membership. There was a man in front of me in line who from what I overheard of his conversation with the manager was returning something like his 5th tv in a year. The manager gave him his refund and then rescinded his membership and had the man walked out of the store.

The secret sauce: Costco sent that TV back to the company who sold it, and deducted the value from the next invoice.

If Samsung, etc didn't like it, Costco would drop them as a vendor real fast. So the merchants would eat it. Apparently it got bad enough that they stopped eating it.

Well I think most people would not return in this sort of scenario.