We rented a car in Austin, Texas from ACE Rentacar and upon taking the car we did an inspection. In addition to what they had listed as existing damage, I found a broken shroud under the front bumper and I pointed out a rock chip on the hood. The attendant was standing just behind my left shoulder when I pointed it out. My mistake was to say something to the effect "I don't know if you want to put that down".
Well, he didn't and when we returned the car a different attendant made note of the rock chip and wrote it up. A month later we get a bill for $558 for the repair of that rock chip. I wrote a letter to them describing the incident and they continue to insist that it was new damage.
With that in mind I suspect that they either didn't follow up with the original attendant, that he lied or didn't remember. I suspect that it may even be their unwritten policy to not mark anything that the customer doesn't insist upon noting in order to come back and hit them for the repair bill. That was my mistake and one I won't make again with ANY other car rental company.