http://www.slate.com/articles/life/travel_explainer/2015/08/rental_cars_get_old_what_happens_to_them_next.html

There are rental cars, and then there are kind of old rental cars—the ones where, during the initial walk-around with the agent, you carefully point out a scratch on the back door or a small dent in the hood, just to be clear that the blemish predated your term of use. But what happens to a rental car when it gets actually too old—when the days and miles and scratches accumulate past an acceptable point—and it can’t be rented out anymore?