Avis doesn't hold cars for you. They don't set aside a Corolla for you when you book it in July and hold it til you pick up in October. They hold reservations.

As far as I'm concerned, nobody should rent from Avis or Budget unless you have a corporate agreement with them or they are vastly cheaper than the other companies. I have never waited in line at a major airport with Hertz or National because of their choose-your-car setups. Avis just can't compete.