The operating philosophy of Costco is simple: keep costs down as much as possible and pass the savings onto its members. Since Costco has such a large membership base and immense buying power, members ultimately get the best possible prices. Costco is able to keep markups low due to making most of their earnings on membership fees.
A key selling point of Costco is its private label brands, such as Kirkland Signature which was launched in 1995. These private brands are comparable in quality and will always cost less than brand labels, it is no surprise that these brands generate 20% of total revenue.