Wal-Mart has been dogged by criticism of the standard of its stores in recent years, including long checkout lines and insufficient stocking of its shelves. Over the past decade, Wal-Mart Stores Inc (WMT.N) opened nearly 1,500 new stores in the United States, a 45 percent increase in space and equivalent to more than 4,000 American football fields, while its sales have grown by 50 percent.