What does costco do?
Costco wholesale is a membership warehouse that offers direct to consumer pricing for products bought in bulk.  The majority of Costco's revenue is generated from memberships not from the products they sell.  They also offer brand-name merchandise at steeply discounted prices.  With a Costco membership you can also purchase products online directly and have then shipped directly to you.  Competitors to Costco are Sam's Club, Walmart, Amazon, Kroger, HEB, Home Depot, and Lowes.