When I look at any product I (usually) only look at the negative reviews. For most products, I found that I need to be discerning.
Some reviewers are looking for diet products that allow them to eat cheeseburgers and see weight loss, and are disappointed. Others will claim to eat right and exercise with no results. If you eat right and exercise, it's science, you'll lose something. These two types of reviews aren't helpful.
Sometimes the positive reviews will list pros and cons, these are the most helpful.
Right now I'm looking at something recommended by Dr.Oz. Turns out it's far from a new product, and being marketed under a new branding. The only new thing about it is some newer research findings...and the most interesting weight loss benefits are a theoretical, rather than sound clinical trial based results.