In my experience most “builders” when they appear to be ripping you off or lieing do respond to being stood upto . I use the exact language that I can’t use with a tenant who is confrontational. It’s very therapeutic to release all that frustration and anger . You also effectively drawing a line in the sand . Then it becomes shut up or put up . I know confronting people and potentially the risk of that becoming physical isn’t appealing , no one wants that . But it’s YOUR build , YOUR money - take control ; whether you are wrong or right . Alter the course of the builds destiny relies solely on you making it happen . ??