Pay other's damages

Car collected on 19/10/15 at 13:00.later that evening realized it had tires faults. Called call centre at 19:30 that evening. Was told to return to the branch to get replacement. Polo was given at around 20:45. NOT CHECKED with me. Now Avis is telling me to pay for a scrach that had been there when they gave me!. Is it not fact that they must check their car with me before handing it out? . I refuse to pay for something i dont know