Many items on Amazon come from third-party sellers on the Marketplace, indicated by a "Sold by" line near the "Add to Cart" button. If both Amazon and third-party sellers offer the item, the large "Add to Cart" button buys from Amazon, and you'll see a few alternative "Add to Cart" buttons with different prices and a link to a full list of used and new versions of the product. Marketplace sellers set their own prices, so you might find a great discount on a used item, or come across a rare, discontinued product that's only for sale at a collector's price. Even when buying from another seller, Amazon itself handles your payment, so you don't need to worry about your credit card information leaking out.
The infomercial industry is huge and is worth a staggering $250 billion as of 2015. It all started back in the late 40’s and early 50’s when major sponsors of serial television programs were soap manufacturers (i.e. Proctor & Gamble, Lever Brothers and Colgate-Palmolive), which is how “soap operas” got their name. There is some controversy although the first infomercial is thought to have been for a blender either made by VitaMix or Waring Blenders and aired in 1949 or 1950. Time limits for commercials were imposed by the Federal Communications Commission (FCC) not too long after this which halted the growth of infomercials until 1984 when those limits were removed.