I recently ordered some junk food from Amazon, despite my wife's objections. I ordered it from an Amazon Market (aka third party) seller since that was the choice picked by Amazon for one-click ordering.
The food arrived, and the interesting thing is that it arrived in a Walmart box, with a Walmart packing slip. Evidently, someone savvy recognized that the Walmart price was lower than the Amazon price, and undercut Amazon's price using Walmart as the fulfillment. I was pretty annoyed to have been caught by this, but at the same time I have to respect that they pulled this off, and that I got the food cheaper than if they hadn't done this.
Anyway, just thought that it is interesting that people are out there doing this!