Who said it again?

Totally disregarding an argument based on who said is called "mistaking the person for the argument." In a way it's like the "Boy Who Cried Wolf" story. The boy went around saying there was a wolf trying to eat the sheep and people would run and panic only to find nothing there. Once a real wolf came, no one believed him. If he argued that wolf came and ate some sheep, people would reject him because he said it. You must consider the claims to be true or false in a non biased manner. A phony refutation when someone makes a point that the person who made the argument can't be believed because he hasn't been trustworthy in the past. In the case of the story, people reminded the other town members that he had told this lie several times. There's a company that sells vitamins, but they are known to scam people through a pyramid scheme, but you can't use that to disprove that the vitamins are actually valid.