Avis Rustenburg - shocking

I would just like to warn anybody when renting a vehicle from Avis Rustenburg branch. My insurance company arrange my rental at Avis and I went to collect the car. We went with the Avis employee to check the car, but nobody checked the grill under the car, not us, and neither did the Avis guy. We were advised about an insurance that we could pay a little extra for incase of any accident, wheel or windscreen damage, but we were not told that the R500 waiver you are told about does not include an extra 849.00 apparently for admin and extra's from somewhere. Firstly when we returned the car the lady that went to check, checked the spare wheel and then went straight to the front and checked under the front grill and told us that we would have to fill in a report as we have damaged the car. I really feel done in by Avis, and never want to deal with them again.