I have used Avis in the past and had a mixed bag of experiences. I always video me going round the car in the parking stall incase they try anything and also pay using a CC with a low credit limit in case they try hitting with additional charges.
Fortunately never had a really bad experience but Thailand Avis (Franchise) was nearly an extra charge when a hippy stole the hub caps off the hire car!!
The USA is when I go through the terms with a fine tooth come for the reasons that others mention above. I dont find this just related to Avis though as an industry I find most of them try it bizzarely my two best experiences are with Advantage of all people and Sixt