Ok I have a bit of a thought about Public Rating. Perhaps an extra thing you could do would be to allow accounts to submit ratings, but only actually count/submit them when the user has also rated 2 other games. That way, more games get votes, the voter gets a wider sample pool by which to base their ratings, and it makes it so users can't just instantly make an account and rate a single game. It also gets them more involved in the Itch ecosystem which is nice!
Viewing post in JSON export of jam results + results discussion
Yeah - public voting in large jams will be an issue as people can naturally get competitive or worried about not being validated by reaching a high enough rating - I think either way being able to check whether a person is just downvoting other submissions (perhaps if many times they've voted far below the mean of results) would be an interesting safeguard, or making it so only Itch accounts of a certain age can vote (e.g. were created before the jam started, or before voting started) but ultimately any form of public voting whatsoever on the internet is going to have to rely on trusting everyone involved to an extent.