There are liquidation companies all over the country that get truckloads of what they call "shelf pulls" which are what we call "penny items" as well as returns. They usually auction off the merchandise and charge a percentage of the sale and thats how they make their money then the profit goes back to the store/company that sent them all the merchandise.
There are a few around here that list brand new in box items all the time from shelf pulls and it used to be worth it until they were advertised on a local news segment. I got a few items for 80% to 95% off but now so many people know about it there are people dumb enough to pay full price or more for items.
They dont advertise where they get the merchandise from but I can tell they get stuff from amazon, costco, sears, home depot, staples and many more. They even have the option to buy full truckloads and provide a manifest of what is on the truck before they unload it to auction things individually.