It depends. In the UK, my rentals are scrutised very closely when they're returned. If there's so much as a stone-chip, they usually point it out and threaten to bill me for it.

In the US, though, I've noticed that normal 'wear-and-tear' -- meaning parking lot dings, small scrapes on the bumpers, etc -- are normally not recorded. When you return a car, they're generally looking for something hanging off. If you weren't charged when you returned it, I suspect you're probably in the clear.

I rented a car with Hertz a few weeks ago. I spotted some scratch damage on the right side of the car, but the rest seemed clean. Still, I had just arrived on a long flight from Europe and didn't scrutinise it too closely.

The next morning, I noticed scratches on the LEFT side that were much larger than those on the right. While I'm absolutely certain I didn't hit anything, I can't rule out the possibility that someone hit my parked vehicle. Still, since I wasn't genuinely sure whether the damage happened during my rental or previously, I decided to return it without saying anything. Sure enough, the rental return agent didn't bat an eye.

YMMV.