Unless you are in this boat, you are probably doing more damage than good.
How?

Let us start with the almighty, all-consuming behemoth that is "the algorithm".
All major shopping platforms will implement an algorithm internally (although more likely, externally, so you buy more). It can be as simple as tracking what products sell well, are likely to sell well in the future, all the way through to recommending you every single piece of Harry Potter memorabilia under the sun, because your wife is a fan and you got her something nice for her birthday.
Metadata based on product reviews are factored into the algorithm to determine it's weighting to display in the marketplace – a product with good reviews can rank higher in the store listings, even if it is up against a product that has sold more, but has a weaker review score.

Now, dear reader, you might be thinking – so? I read the content of the review to determine whether a product is a good fit for my purposes. Great! That is what you should be doing when researching options. But not everything is about you now is it?

The very livelihoods of hardworking people are inextricably linked to your (or someone else's) decision to hit 4 stars instead of 5. Consider this scenario: you've just purchased a locally made jam from a major shopping platform. Having done your civic duty by paying a bit more for the one made by a family company, you try it and think it is sublime and you remember this fact when it comes time to fill out the review form when the reminder email shows up.

You think to yourself, it was excellent and click 4-stars, because you only save the full 5-stars for things you simply cannot live without (or worse, things that you blindly love despite it's flaws, but brand loyalty has made you it's slave).