We always buy and travel with the GS Campground Directory. The rating criteria is published in the front of the directory. Several times we have taken the rating sheets and rated the campground ourselves. Each time we've come out within one point of the rating in the book. You may not like a campground based on your criteria, but the GS rating has nothing to do with how you feel or how you're treated or whether you liked the owner or the neighbors dog. It's a very specific and objective rating system. Since we are in a Class B, the star rating on the restrooms is the most important rating for us.
I suggest anyone who uses the ratings as a guide do this a couple of times. It helps the user understand the rating system and how to use it to pick a park. For example we generally look for a rating of 7 and above with a restroom rating of 8 or above with a star. It's worked for us. One time we thought the restrooms were not worthy of the star rating for cleanliness. Then we realized it was he last day of a holiday weekend and we were lucky to find a site anywhere. Again, I suggest you use the criteria to rate a couple of parks yourself and see how he system works.