Welcome to MPGH! as you have seen the market place has many services and many things being sold everyday.
Money Making Ebooks work but only as much as how hard you are working. I've bought 2-3 ebooks making money in my time and none of them have really worked. Your best bet to make money is buying something you know that will sell from amazon like a PS4/Xbox One and selling it on like ebay or something. Amazon refunding works charms but I suggest you do a bit of research on it before you start making some big moves.