There is something about the FB platform which seems to bring out the worst in people. I have long-term friends who I always felt were pretty stable, rational people, but over the last couple of years some of the garbage they post on that platform was pretty disappointing. I've had to mute a couple, unfortunately. It also seem the larger the scope of the FB page, i.e. businesses in a popular industry, seem to exponentially attract more trolls. I too left the AG FB group after only a couple days. However on the opposite end, my local SCCA autocross chapter seems to stay very civil, and to a lesser extent the city-wide Cars and Coffee page (which I think is very surprising).
I've come to the point when seeking important information or have the need to discuss a topic, FB is the LAST place I'll go. It has become one of those places where nothing good ever really happens.
As with anything, 'intelligence gathering' on Facebook is only as good as the source (person) providing it. While the Autogeek Facebook group is certainly the wild, wild, West of social media detailing groups, occasionally valid info can be obtained if one can distinguish the validity of the source. With nearly 40k members, there's certainly gonna be some 'good apples' among the yahoo's. Unfortunately, the noise generated by the yahoo's and the pretenders will drown out the decent contributors as they generally will post a tidbit of info and then essentially 'go away', not responding to any further disagreement or disparagement of their posted information. These are folks who are not often swayed by the 'Flavor of the Month' (Beadmaker, anyone?) and provide information with enough detail to make a reader pretty sure they have actually used the product in question. Unfortunately, based on volume of posting alone, they are often drowned out by self-proclaimed experts, some of whom I suspect have not actually used many (if any) of the products they say are the greatest thing on earth; never any specific detail of product use, never any pictures, 50-50 shots or even bottles or product descriptions outside of what you find on the Autogeek online catalog. I've seen the self-proclaimed experts advise a relative newcomer that removal of a consumer coating involves wet sanding, no if's and's or but's; imagine if someone took that as gospel and went at their coated hood with predictably horrific results.
The Autogeek Facebook group is one I follow; heck, I enjoy reading *anything* on this topic although if trying to answer specific questions on things I know I have a somewhat firm foundation of experience in, I often do it via private message to avoid the resulting nonsense of 'brand champions'. I do get some pertinent info there on occasion and I'll usually check the posters profile to see if they have any other evidence of experience. It's a starting point at the very least...if you can tolerate the nonsense.
Aside from the chaff, there are certainly some decent groups available on Facebook although they are fewer and generally strictly moderated. There's a coating-specific group that is filled with mostly professionals and those guys don't mess around; pretenders and trolls are generally outed quickly (and politely) and soon disappear of their own accord as their personal agenda doesn't work well within a 'serious' group; 'know-it-alls' need not apply.
I use Facebook mostly in a passive fashion, following manufacturers and a few groups although, given the right mood, there is entertainment to be had in some groups. I think I joined back in 2012 and currently have less than 20 'friends', 99% of which I have turned off seeing their daily postings as one can only see so many cat, dog or baby pictures. It is generally the lowest common denominator when seeking valid information though; I don't easily understand why some turn to Facebook when a simple Google search would cast a far wider net.
Still, an occasional nugget of 'goodness' can be found if you're willing to sift through the trash...YMMV