I used to just open YT WH videos, pop a thumbs down, backtrack to the gallery and open another, rinse/repeat. I noticed that if I went back to them a few days later my downvote was gone. So now I open them in new tabs, let them all play a considerable amount, then run thru downvoting and closing. I think they're looking at downvotes made very early without watching anymore of the video and negating them.