This is a big advantage for both customers and the company, since it allows Costco to sell its products for razor-thin profit margins, sometimes even at a loss for a particular item. Costco reported a big increase of 6% in comparable sales excluding the negative impact from foreign exchange fluctuations and gasoline price deflation during the 22-week period ending Jan. 31, 2016. Both Wal-Mart and Costco offer some attractive traits for investors, and the right decision would depend on your own risk tolerance, investment philosophy, and your vision of the future for the two companies.