Your criteria for rating may be different. The GS guide is based on several criteria that you might not consider. Also parks have good seasons and worse seasons in the year.
Those of us who like natural settings, vegetation and room between the sites would give a 9 or 10 to a cg with those attributes. We would also give only a 2 or 3 to a cg with a sardine parking lot for sites and concrete everywhere. Hence the difference in scores at rvparkreviews.
If you want to understand how Good Sams rates the cgs, read the info at the front of your guide. You can also read it here
http://blog.goodsamclub.com/2010/11/how-are-good-sam-rv-parks-rated/