I had an experience last year with the Avis location in downtown Atlanta.
I can't speak to other Avis or other rental car company locations, but what apparently happened here is that this location uses a literal hand written list of daily rentals - and my reservation # was switched for someone else's by mistake.
The consequences were Kafka-esque as well as comical:
1) The car I was supposed to get as notified by text, was not available as it was apparently given to someone else. I instead got a ginormous 4x4 Ford F150 truck - just what I needed to drive 600 miles from Atlanta to Charleston SC to Hilton Head SC and back... And I got this car after sitting in their office for 1.5 hours because they basically gave my car away to someone else. It was apparently graduation week so they were low to start with, to be fair.
2) Emails from Avis now refer to me by the other person's name
3) I never got credit for the double credit Amazon Prime promo; I am not even sure I got credit at all. Maybe the other person got it.
4) I got 2 different notices - 1 for a $12 ding plus $35 in services charges; I just sucked that up without question until the 2nd notice of another $50 charge for a service call. As I never made this service call, I fired up an email to Avis complaining that it is almost certain that they were assigning damages and this service call to me when it was not actually me in the car in question.
5) related to the above - I got 3 different Avis emails with receipts for a credit card charge for my Avis rental. 1 was correct.
So - don't assume that it is computers that are at fault although it is clear the computers made the problem much, much worse in my case.