If an owner is OK with their course being listed, then by all means rate it--and no special criteria just because it is someone's labor of love in their backyard. But IF an owner has stated they do not want it listed (J. Gill, J.Sias), then no reviews, even if it is mistakenly listed. If we do not respect private course owners' wishes, those courses will simply close even to those who know they exist. Especially the nice ones.
The issue, as relayed to me by two such owners, is that once a course is listed, players tend to 'ignore' the private/contact owner first statements. Now you have random people walking literally through your backyard, etc. A vast majority of DG players are fine, but we have all seen courses where a few bad seeds have no respect.
Flip City/Harmon Hills/etc are pay to play and private, yes, but they typically have an entrance area that is manned a good chunk of the time. They are also busy enough so it is understood the course will always have players on it.
Truly commercial DG venues like Maple Hill, Highbridge, Selah (RIP, never got to play), and Eagles definitely are a different breed, they want to be listed and publicized.
The few truly private courses we have played, that don't want to be public, are typically empty. Usually with the owner playing the course with us. Those I will not review here. Though I would love to because they are usually great!