Be careful when you hire a car!

I am physical disabled and cannot check a car from top to bottom when hiring it! The person from Avis who assisted me in checking the car, walked around the car and told me it was scratched at quite a few places, even the wheel caps was scratched. I could not walk around the car with him but I took his word that he noted all the scratches. I hardly drove the car, and parked at my sisters house and then on the Tuesday drove to Cape Town Stadium where I had arranged for the car to be parked right in front of the door in a disabled parking,s o I know for a fact, nobody else could have damaged the car in any way. I drove from there to the airport and when the Avis guy checked the car, he found 'new' scratches right at the bottom (nearly underneath) the car - this could not be spotted unless somebody bend down to check it. I immediately complaint about it, but the guy said sorry, I must write on the paper that I did not do it and that I am disabled and could not have checked it, and they will contact me. Nobody contacted me, and I was billed over R900 for something I did not do!! Please check the cars PROPERLY when hiring it! I am upset as this to me is unfair! I will not use Avis again