Costco doesn't make money on what it sells inside; it makes money on the entry pass.

Costco runs membership warehouse clubs: 924 giant warehouses where 81 million members pay an annual fee to buy at rock-bottom prices. The margin on product is barely 13%, almost token; the real profit lives in the membership fees, which drop almost entirely to the bottom line.

Member renewal runs around 93% and delivers the bulk of operating profit. That loyalty comes from a simple pact: sell genuinely cheap, don't squeeze the customer. A rival would take decades to build the same purchasing scale and the same trust; the thin margin isn't a weakness, it's the moat.