Vulture ran an article on September 2023 that raised criticisms including the fact that since the acquisition by Fandango in 2016, the rules have changed in ways that happen to favor the biggest movies. The article cited publicity company Bunker 15 as an example of how scores can be boosted by recruiting obscure, often self-published reviewers to write positively, or selectively hiding negative reviews, using the example of 2018's Ophelia.
Try searching for barbie movie for an example. Click more reviews and filter by 1 star. The third says:
"Barbie," director and co-writer Greta Gerwig’s summer splash, is a dazzling achievement, both technically and in tone. It’s a visual feast that succeeds as both a gleeful escape and a battle cry. So crammed with impeccable attention to detail is "Barbie” that you couldn’t possibly catch it all in a single sitting; you’d have to devote an entire viewing just to the accessories, for example.
It even says ADVERTISEMENT in capital letters but below the fold where you have to expand the whole review to see it. Despite that this review directly contradicts its star rating, 774 "people" have marked it as helpful.
Scroll down a bit further and there is another, "If this was an item on the McDonald’s menu, it would be everyone’s favourite - the Oreo McFlurry. Hands down, I don’t think I could name a better film. The acting was superb!" which supposedly nearly a thousand people found helpful. This one doesn't say anywhere that it's an ad.
When I first noticed this, almost all the top 1 star reviews were ads. Real users have been correcting it and the top two reviews are now real. The second review says "Update: if you notice google is showing mostly 5 star reviews when there is almost an equal number of 1 stars to 5 stars hence why the average is 3 stars." and the 5th post says "I noticed a few giving spectaculars about the movie but rating it as one star, maybe to drown out the real reviews?" so irate users have been noticing the manipulation too.
It's really very embarrassing for Google. It's gone now but originally when you searched for this movie there was a special pink sparkle effect. So they're paying engineers to write special code just for this movie whilst ignoring obvious fake reviews, claiming they were meta-reviewed by thousands of people and they still haven't cleaned this up even weeks later.