Some stores such as Costco have unique sales models in the fact that their main source of revenue doesn''t originate from sales. What they earn most of their income from is membersh.i.p.s. Their membersh.i.p.s prices are pure profit, whereas their products only need to be slightly profitable if at all to sustain their business model. Even their restaurant products (finished food products behind checkout) are especially cheap inorder to attract more customers.