The best niche finder is usually the brain. Also, if you are looking to set up a website for selling products, it would be useful to have some knowledge of the product before you start it. You could just look around you and think of what you like to do, it will also be a lot easier for you to write articles that way.
Another way of setting op a website for selling products is becoming an Amazon affiliate, you redirect them to their products and receive a commission for every sale.