Charge for dent already exist?

My wife returned today and enterprise said there is a dent on rear fender which my wife checked with them when pick-up and they said no problem since it is small.
There was no proper size car, so rent one just returned. They didn't clean with no walk-down and just told my wife to bring it. But we already had a bad experience before, my wife checked by herself and asked them to write. But they didn't record only that thing. The car already had many dents on the body and damages on RIMs. It was a dirty car.
Shocked,nothing to say, and their repeatedly saying they can do nothing but believe the contract signed by wife. So I tried at least to make the report very clear. When I asked them to correct the report 5th time, they kicked us out of the office since we spent 45min already. Where is the rule? So we walked back to the colision center to pick up my car.
Manager said it will be only 200 bucks so not a big deal, OMG, it is not my fault, why I should pay?
FOr enterprise, You need thoudsands of photos and video of whole rent process. They say car is perfect with no inspection and check for hours when return for money.