Vainamoinen: It's either that for GOG or providing other, possibly more costly safeguards against review bombing. For certain publishers, developers, and games, "doesn't own the game" means 95% fake reviews. I've attached a recent example. GOG will of course display the overall rating more prominently than the verified owners rating. From their business clients' perspective, that's horseshit.
Even more heinous of course is when fake reviewers downvote positive reviews, which also happens here 24/7.
Not to sound flippant, but of course user game reviews are as subjective as humanly possible. It's art criticism, plain and simple. There's no one objective measuring stick for that. Yes, they are often "not worth a pinch".
They are also indispensable.
GOG is now pretty much fighting for survival.
Despite my healthy skepticism of reviews, they are as you say, somewhat indispensable. I just be really discerning when I read them, and maybe I just go for an overall consensus if there is an obvious one ... even then though, I sometimes look elsewhere for important info about a game I am interested in.
Often for me it is weighing up all the factors that are available, and reviews are often just one part, so images and video clips and even the blurb can be more important ... even the game title. The file size of a game can be quite telling also.
As for the review bombs you speak of, I cannot say any have ever really stuck out to me, so I am very skeptical about that. And having gotten over 1600 games from GOG now since May 2017, I have seen and read a lot of reviews.
Anyway, I always check if the reviewer is listed as owning the game, and always give more weight to their review if they do. And any review that starts to sound opinionated gets short shrift with me.
The very real truth, is that unless a game is exclusive to GOG, many more folk at Steam and elsewhere would have bought and played the game, and their reviews can be quite valuable. And it seems very unlikely to me, that many would deliberately post at GOG just to be negative about a game.
What actually bothers me more, is folk who have a connection to the developer or publisher spreading misinformation to encourage sales. They are the true fakes that to me are quite likely more common.
Are GOG really fighting for survival any more now, than they have been for at least the last half of their existence? To be perfectly honest, I don't really know. Sometimes I think they are, sometimes it seems not.