How A Single Costco Changes Its Local Economy (youtube.com)
The Honolulu store, Costco's biggest, did half a billion in sales lasy year. Stores nearby close, over time wages are pushed down.
Costco breaks even, if you factor out the memberships. They pay workers higher than those workers could get otherwise without a college degree, but those workers can't increase their salaries unless they get a college degree.
Locals buy more expensive items after Costco brings in higher pay, so they don't need the budget items anymore.
Costco only maintains 4000 items (SKUs ie stock units), compared with Walmart's 140k.
Small businesses buy from Costco and resell. They use Costco's shipping.