Credit hacks dissected: Do these really work?

My buddy Alan sent me an email with some interesting credit hacks: “1) If you have a short credit history (like me), get your parents/grandparents to add you as a authorized user on their oldest credit card (you inherit their credit history length) 2) If you have any blemishes in the past (like a single missed payment when you first got your credit card in high school) dispute it right before making a car/house transaction because while that blemish is investigated, it is not counted against