There have been plenty of verifiable examples of both paid likes and paid dislikes. It's even obvious from the metrics, so they COULD do something about this even with automation. At least for relatively large channels - sorry, your subscriber base doesn't suddenly go from less than 1% of your viewers being in say Vietnam to suddenly 10% who all happen to hate your video. Or like it. Same thing, it is so blatantly obvious that these are paid shills.