I don't think I brought up Costco's wage/salary policies as an example of how they can differentiate themselves from their competitors. My point was that big retailers don't have to pay rock bottom wages to remain competitive and profitable.
You, or someone else, brought up that Costco's customers and markets are more upscale than Walmart's normal customers and markets therefore Costco can afford to pay its employees more. But that ignores 1) Costco's margin, posted by Axulus earlier, is 2 percentage points lower than Walmarts and it is still a successful business, and 2) Walmart has
recently announced it is raising it's payscale for the bottom tier employees by a significant amount. So it appears the different scale of clients and markets weren't the real reason Walmart was paying unlivable wages.