The items listed below are the key things you should look for before joining Product / Service Reviews Websites. Pay close attention to these areas as they determine which sites are the best.
User and Editor Reviews / Comments
Look for product / service review sites that offer both user and editor generated opinions and reviews. This ensures that you get the "expert" view as well as the consumer view, after you which you can decide which one has more credibility (hint, the customer is always right).