Sarah, who is an excellent mechanic, said that in her opinion the used car John is considering is in good mechanical condition  However, it is clear that Sarah cannot be trusted to give an honest opinion, since when Emmett asked her opinion of his new haircut she lied and said she thought it looked good
Ttherefore, it is very likely that Sarah also lied in giving her opinion of the mechanical condition of that car
It presents evidence in value-laden terms that presuppose the conclusion for which that evidence is offered.