Ok, so over at r/budgetfood I host a weekly challenge. At first I would determine a winner by looking at RES total upvotes and ignor the downvotes. Then I learned that those numbers were just "estimates".

A user suggested that they could vote by posting a comment as such. You could just require users to comment with a header "-Vote-" within the comments of each post. The downsides are that it requires an engaged user base that wouldn't mind posting a comment to vote.