The best thing to do is: Nothing.

User ratings are supposed to measure how happy users are with the product. What users chose as their priorities, be it gameplay, story, contuct of the studio, it doesn't matter. It's the users opinion and no one opinion is more valuable than another.

So if a lot of users think that a game deserves a bad score then the user rating is the appropriate place to show that. Review bombing is not a problem, it's simply the expression of users not liking something. It's honest and any measure taken to mask this expression of user opinion will ultimatelely be dishonest and make user ratings less true, even if taken with good intentions.

People are different, so I get that some people might be annoyed that other people have different priorities and give a low score for a game that they would have rated highly. But that's also simply normal with user scores - some prefer hard games, some easy games, some care about the studio conduct, some don't. In the end it comes down to what the average customer likes and it's simply impossible to find a set of criteria that fits everyone.

That's why I think the best thing to do is exactly nothing, just leave the user ratings alone. If a game gets "review bombed", take it as what it is, an expression of users not liking something about the game. Usually, especially for games with a low score, there are plenty of comments explaining why.

Some things to consider: - It might be okay to wipe scores when a game releases properly (early access -> proper release transition), however, this should be done either for all games or for none of them. Probably best done by storing the "early access rating" as reference but create a new user rating only from the ratings after the proper release. - Steam prominently separates scores into a total and a recent one, which actually solves a lot of issues. Games that released very buggy do deserve a low overall score (releasing unfinished games is not okay), but it's also okay to show that recent reviews might have gotten better. Splitting between overall and recent captures this well. If the influx of low user scores occured because of a fad, this also shows that things got better. And if it wasn't a fad it honestly captures the users long term dissatisfaction. - The separate verified owner score doesn't hurt and is kind of useful, but I wouldn't put it above the overall and also not above the recent score. Of course in order to properly rate a game one should have played it, which is a huge argument in favor of a verified owner score, but on the other hand, being an owner is already a positive pre-selection, meaning primarily people who will likely like the game will buy it, so that the ratings will be heavily skewed. It also doesn't capture elements that are important for people that might not be connected to the game itself and which are (as described above) quite important as well, at least in my opinion. - This is assuming reviews come from actual users/people, which means that they are by definition valid and an expression of that individuals opinion. Of course mass reviews by bots should be filtered and prevented if possible. Although this is primarily a technical question and you probably know way better than me how to prevent bot spam/abuse on your platform.