Edited for update 9/6/22 - see bottom for update...
We originally booked our reservation in December at a total est cost of $620. In March we "modified" our reservation by 2 days. Instead of honoring the original price for the original timeframe and adding 2 days at March's rates, Avis cancelled & rebooked the entire reservation at March's rates. Thus, by adding the 2 days to our reservation, Avis requoted us $1480, making the additional cost $860 or $430/day (not what I would call a "modification"). I did speaking with cust serv at the time, but got nowhere.
Additionally the car we received seems to have an issue with its alignment. It had a noticeable and annoying shake to the entire car when going between the speeds of 40-60 MPH. It definitely needed to be serviced. When we picked it up, it seemed clean (dash, seats, carpets were all clean), but it was soon evident that the inside of the windscreen was filthy. It was very difficult to look through with the sun directly on it or, worse, at night with other cars coming from the opposite direction with their lights on. We had to purchase cleaning supplies just to clean it so we could drive safely. Further, I dropped something between the center console & the driver's seat and had to move the seat to retrieve it. When I did, I found 2 used coffee cups, a McDonald's cheeseburger wrapper, a handful of french fries and several other food items that i couldn't identify. I then found similar (but not as much) items under the passenger seat.
Lastly, the front passenger door had something wrong with its weather stripping. At speed, it was constantly making whistling sound. For a 2-4 day around-the-town rental it wouldn't have been a problem, but we had the car for over a week and put on over 1200 miles, much of it highway. It was a constant distraction, and all 5 of us were annoyed with it.
Please note that our issues with Avis are directly related to it's poor rental policy and the vehicle we were assigned. Avis employees were all helpful and pleasant.
Update 9/6/22 - On 8/24/22 a Territory Performance Manager (for the area in which we rented the vehicle) contacted me by email within a day or 2 of completing their customer survey, which echoed the above issues. He apologized and offered a $200 credit for our troubles with Avis and the vehicle. He also stated that he could not "see the original booking", which intimated to me that he would be willing to look further into honoring the quoted price of the original booking. I replied by sending him both confirmation emails I received - the 1st for the original booking in December and the 2nd for the Modified booking in March, and asked him to let me know if can do anything else for us. I have not heard from him since.
On 8/31/22 I received a response from Avis regarding the above Google review asking for our rental number so they could look into it further for us. I replied by letting them know what the "Territory Performance Manager" said & did as well as providing both confirmation emails and ask them to look further into honoring the original quoted price. I received a reply on 9/4 confirming that Avis' policy is to change prices to current rates with each modification (not their words, but paraphrased), that the $200 credit will be processed followed by the usual fluff - we're glad you brought this to our attention, this does not reflect Avis' usual high standards, a report has been sent to the manager in question, etc., blah, blah, blah.
As such, we remain unsatisfied Avis customers. No doubt that the $200 helps, but with that, it reduces the additional 2 day additional rental cost to $330/day which is still ludicrous.