I've had similar issues renting cars from Avis at SFO. Once reserved a mid-size and ended up with a Toyota 4-Runner that flat tired after five days. Ironically we got the flat tire on 101 800ft from the airport exit as we were returning the car. Spent 30 minutes on hold with Avis when calling for assistance, only to give up when a free NPO road-service vehicle spotted us and stopped to help.

Another time I went to Avis at SFO without a reservation only to be told they had no economy cars at all available, only large, sporty or high-end cars with a price tag to match them. I declined, got to the back of the line and booked a Toyota Corolla on my iPad at half the price I was quoted for the other cars, and ten minutes later I was driving out of there with a car they supposedly did not have.

I booked the Corolla for five days, but called to extend it anther two days. They never charged me for those two extra days though, which makes me wonder what state their car administration is in.

I'm done with Avis.