I think it is going to be a lot more common to find minor damage on rental cars as the fleet gets older and older. I think the days of getting cars with under 500 miles are long gone.

Fortunately the company I work for has a contract rate that includes CDW so I don't have the fear of being charged for any exisiting damage. I do still look for anything glaring.

I know there would be no easy way to do this, but it would be interesting to see how many times the same "damage" is billed to several customers. Again, I am not saying any station is doing this, but it would be very easy for a less than ethical company to do this and never be caught.

Of course just thinking about how easy this would be to do might also convince you to purchase the waiver, so the company wins if you think you might be scammed. Talk about win-win for the company and lose-lose for the customer.

Back to your situation, you did the right thing in telling them, I would forget about it unless they contact you, which I doubt they will, and if they do tell them the truth, you didn't cause it, and it was a high mileage car (although 36K isn't as high as I've seen on other cars). Tell them you already discussed the situation with them, and consider the matter closed. If they start pushing the situation, push back, but again I doubt they will. The car has probably already been rented to some other poor sap who is now thinking the same things you are thinking.