alt Hacker NewsI see you're not terribly familiar with Costco. Membership fees account for the vast majority of net operating income for Costco and they keep markups on items at no more than 14% over cost (15% for Kirkland brand).
So yes, Costco does make most of its profit by ensuring customers are happy and continue to renew their memberships every year.
>Membership fees account for the vast majority of net operating income for Costco
This is financially illiterate because you're mixing revenue ("membership fees") with profit ("net operating income"). While it might be tempting to assume that membership fees is pure profit for them, it's not, because people only buy memberships because they're useful for something (ie. shopping at their stores). Therefore you can't strip that out from the other costs associated with operating a chain of warehouses.