"Точно?" just means you have doubts in what you've just heard. Sometimes you can add the details, like in "В центр идёт десятый трамвай" (Tram #10 goes to the centre) - "Точно десятый?" (Are you sure the number's 10?)

"Точно?" is used with the facts, not with the views or opinions. If someone tells you that it's -10 outdoors and you'd better wear warm clothes, you can reply with "точно?" if you don't believe it can really be -10. Yet if someone just tells you to wear warm clothes, you cannot use "точно?" in your answer.