How does this relate to a blog on health and fitness? It's simple... before you jump in and purchase a product based on "false" promises, face value, or some amazing advertising, you should research that nutritional supplement or product. Take a look at what's under the hood and not just skin deep. Oh, while I'm at it, consider self-development and self-analysis. Many just go through life day-to-day, going about their actions, without really having the understanding of why they do what they do. There are plenty of books, The Ennegram by Richard Riso is a great place to start.
To continue, those in the supplement industry tend to have anecdotal evidence, or loosely correlated data that claims some magical pill will make you lose weight or get ripped. A significant portion of these studies are conducted by their teams and their resources without third party verification. Also, beware the reviews. For example, there is a weight loss company that has fantastic reviews for their supplements on amazon. However, they also offer a free-bottle if you publish a review but ask that you contact the company if it's less than 5-star before posting.
Look at the science behind the product. See if it has third party verification. Don't take it at face value. This is why I have been promoting IDLife. The science behind the products can be weighed and measured, it can be studied. Research the products yourself, don't take my word for it.