I had a look at the API, but there are a couple of problems.
As far as I am concerned the API is mostly intended to do fancy things with your own games. Quickly changing prices making an auto reply bot things like that. It is complete overkill for simple get requests.
It also requires the users to accept one thingy (I completely forgot what it's called). Long story short, I can't force this and it doesn't give me anything that I could use for my purpose.
I am unsure how I would even go about implementing your post suggestion. Write a silly comment? I don't have access to the server, I can't make a popup and lock the ratings.
Also I am new to APIs and the documentation is way too hard to read/implement. Maybe I'm just dumb again and its super useful, but my workaround is fine.
I don't know about requesting the state of every user and game constantly. Firstly it took me about half an hour to collect all data by itself, too long it would let peps slip thru (I might optimize it to make it faster, but it mostly depends on the internet connection that I can't change). Secondly I think that itch.io would kick me for attempting to dos their server
Also the automatic ranking system already nerfs suspicious ratings. They look at all the star ratings you gave and shrink their wight if they don't follow the bell curve. This means that "randomly" clicking (humans can't click randomly) on stars or review bombing in disregard of the game you will probably result in an uneven distribution, which in turn results in your ratings having zero weight in the final score. Cheating that might be more difficult than actually playing the games.
Besides this isn't really what my cheater detection was about. It's more about low effort comments copy pasted to dozens of games. That's what I wanted to detect. People that just want to get you to play their game and don't want to put in the necessary legwork.