Reddit isn't completely a black box: subs such as /r/undelete and /r/longtail track deleted threads, and deleted comments can be reviewed ( https://www.reddit.com/r/howto/comments/5en53l/how_to_see_de... ). Additionally, the disparity between upvotes and comments -- especially for threads upvoted far more than their peers -- can indicate when voting shenanigans are taking place.