Should you buy the shares even at a richer valuation? Costco Wholesale (COST 0.43%) traces its roots back to the mid-1970s when it opened its first warehouse. It has since evolved and become a popular place for members to shop. The business has done incredibly well, and shareholders have been amply rewarded. Over the last 10 years, its shares gained 588%, easily trouncing the S&P 500's 184% increase. While Costco has been a very successful company, retailers can't rely on their past or their reputation. Ban ...