Realistically, if the car is as worn & beat up as OP says it is, it's a scam. I've had to fight with clerks at the exit booth before over damage that they refuse to mark off. Often, they'll say, "oh, that's nothing, we wouldn't ever charge you for that." The harder they fight, the more suspicious I get.

I've been scammed by Avis before, but only overseas. I had an agent at BRU walk up to the car at check-in with a mirror on a giant stick, and then point out undercarriage "damage" that I must have done to the car. I demanded to be able to take a picture of the damage, which consisted of a 1/2" long scratch under the front lip of the bumper. There was no way I would have been able to see that, even with walking around the car to check for damage.

What do you all do when it's dark? A lot of times I'm renting after dark, and the parking garage or lot isn't really well lit enough to see small damage.