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 offered a full refund for the sale. Instead, they received a $400 invoice for the “repairs” of the water heater and told the frien…