Sometimes it's amazing just how much force a karmic pendulum can swing back with, paying you back for your misdeeds ten-fold. This thread was posted to Reddit's r/ProRevenge subreddit by the avenger's friend, Redditor u/Three-Nations, who tells the story of how their friend got even with a scammer after the scammer tried to cheat them over a used water heater that they had sold. The scammer came back several weeks after the sale, trying to tell the friend that it was not working. The friend off…