PE Ratio. Paying Employees "Too Well" can hurt your stock price.

But labor costs are expensive -- they account for about 70 percent of the company's total cost of operations.

Still, some analysts have raised concerns about the company's ability to post larger profits, complaining that Costco treats its employees and cardholders better than it does investors. Costco makes about 1.7 cents for every dollar in sales. Rival Wal-Mart Stores Inc., the operator of warehouse chain Sam's Club, makes about 3.3 cents for every dollar in sales.

Costco's stock is trading at about 21 times analysts' earnings per share estimates for its current fiscal year; Wal-Mart's stock is trading about 25 times analysts' estimates.