Why today’s smartest shoppers are at Walmart, Costco, Ulta, and Ross

There used to be a clear divide between the people who shopped at Walmart and those who shopped at Saks. Not anymore. Consider the shopper on Walmart’s website loading up on the basics: a 12-pack of paper towels, a few boxes of mac ’n’ cheese, a gallon of milk—all from Walmart’s private label, all cheaper than national brands. Then, into the same cart, she drops a $627 pre-owned Louis Vuitton handbag that Walmart has certified as the real thing. The next morning she swings by Ulta for...