In my years as an avis Manager, I have only three times seen a tire charged to a customer that wasn't inlolved in a collison of some sort. Once because it was vandalized (knife in sidewall) in an admitted divorce dispute, once because a customer went off roading and, if you can believe this, a freaking thorn flattened the tire (tough thorn), and a third time when a customer came back with four bald tires. We were a bit perplexed until three weeks later the police came by to inquire about a car involved in a high speed chase.

If someone has had other experiences, I wouldn't be surprised as its often a judgment call. However I never saw the need to charge for a tire for going flat through usage most renters would consider normal. (i.e. your driving it goes flat and you hit nothing on the road).

examples of times where tires were charged almost always involve some other damage to the car.

Rim bent from debris in road/curb.
sudden emergency stop that causes a tire to burst at the bead and impact (I have yet to see an emergency stop that bursts a tire without impact, but that doesnt mean it hasnt happened).