I worked for anus for years - I know the tricks and fees they charge.
they have a crew of workers who detail cars daily. think it was a few years ago they started charging for detail jobs to customers upon rental returns. it was around 35.00 to 45.00 - could understand if the car had beer spilled or puke in it ! but sand ? come on !! a vacume could pick it up
in mins !! was it big location returned to ,or small piss ant type location ?
contact customer service at avis - about the charge ! see what they say

I did contact customer service...they said there was a ton of sand in the car and they had pictures. When I requested the pictures be sent to me e-mail, they never showed up in my in box. I called upper management and he said they would review the case and pictures and get back with me...my phone has been silent. I have it disputed with the credit card company now.