I tell you out of personal experience that happened last year...
There is a Best Buy and Walmart directly across the street from each other, so I went in to Best Buy because I had to buy something anyway. I walked up to them and asked if they matched prices, because Walmart was selling a DVD $5 cheaper. He said he knew about it, but they did not. I was pretty furious, so I left BB without buying anything, and bought my DVD at Walmart...