AVIS Rosebank taking chances

On collection on my rental car , it is supposedly not AVIS duty to check the car with the customers any longer when collecting and not taking customers through the cars to see for any problems on the car. They basically park the car in the parking lot with a cleaning person there and let you just take the car without any checks. I than noticed a mark on the rear door a couple of hours later in the sunlight but did not have the time to go back and inform than as it should have been done by the avis staff when collecting. When I returned the car I informed the person who was collecting the keys and and I filled out a form to say that the car came with a scratch and no one was onsite to check the car with me and to sign I was happy with the car. A few days later I get a SMS to say I must pay R2700.00 for a mark on the door which was already there! Do they do this to cover up their mistakes and charge people because they haven't done their jobs correctly ? I have dealt with Avis before and the other dealerships have always had someone to check the cars . This is not acceptable and they cannot prove that the car had no mark on it prior to my collection.