I think if you read the forum, Avis does not come across as the most trustworthy or ethical company. So, it seems anything goes - your reserved car might not be there, AvisFirst terms change without advanced notice, etc.
Today, when I returned my car at ORD, the guy behind me had a hole in his front bumper (it seems some cover fell off). Avis wanted to charge him for it. Luckily, he had a pink slip documenting that defect. Now, I wonder what happens with the next guy who gets the car. Would Avis automatically document it or it would be up to the next guy to notice it and document it?