I've been an Amazon customer for more than 20 years. Yes, both the 5-star reviews and 1-star reviews can be gamed. Many 5-stars reviews are fake because of bribery. Many 1-star reviews are from competitors trying to hurt their rivals.
That said, I still find Amazon reviews useful if I read the texts instead of depending on the number of stars. I go to the 3-star and 2-star reviews and read the specific complaints customers are writing about. Some reviewers also post useful photos.
For example, I needed to buy a guest bed for COVID quarantine so I looked for "air mattress" on Amazon: https://www.amazon.com/s?k=air+mattress
Most of those have 5-star reviews. I ignore that and simply read the texts. After digesting some reviews, I learn that all air mattresses regardless of brand suffer from leakage (usually after the 30-day return period). Some recommended getting a foldable foam mattress as an alternative to totally avoid the issues with leaks and broken air pumps. That's what I ended up buying and it was the Amazon reviews that steered me away from air mattresses.