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.