Answer: National shouldn’t have charged you for damage if it agreed to drop the matter. But you could have ensured that the matter would stay dropped with a few simple precautions.
First, as you note, you should have photographed the car both before and after the rental. Be thorough and take several shots of the front, including the bumper and the windshield.
If an employee points to some damage, then you absolutely have to fill out the paperwork — either a damage report or at the very least, a form that says the scratch is “normal” wear and tear and you won’t be charged for it. Don’t take anyone’s word for it. You won’t be able to prove a supervisor told you everything would be “OK” later unless you have something in writing.
Based on what you’ve told me (the paperwork irregularity, too high damage claim) I was equally suspicious of the bill you got from National. The fact that it isn’t being cooperative with your insurance company — at least according to you — makes me think the case may deserve a closer look by National’s damage-recovery unit.
Let me be clear about this: If the car was damaged on your watch, you should pay for the repairs. But I’m not sure if National has proven anything, except that it wants $1,341 from you.
I contacted National. A representative called you and said that upon a “more thorough review of its records” the scratch did indeed exist before you rented it. Still, National dropped its claim.