Google the CG and look at images. Often you will find an RVer's photo album. But agree CGs often limit pics of their sites. My approach to picking a CG is find pics of the CG thru google, see if I can get a good satellite image, etc.
How a CG takes care of their sites is a good way to evaluate a CG and pictures paint a thousand words. To me clean, level sites and lots of pics of them even if they aren't as big as we would like, tends to mean they take care of the rest of the CG.
I've noticed over the last few years COE Cgs are starting to add pictures of every site... Perhaps their standards will influence private CGs to follow.