On a much more minor scale, every time I have rented with Avis, which I now try not to do, my prepaid amount which was sold under UK regulations as the final amount including everything, always attracts an extra $20-30. Every time I complain to Avis UK and every time they admit it's wrong, but they can't do anything except reach out to Avis US who then don't respond. I have thought about a cc chargeback, or a Small Claims Court (absolutely slam dunk under UK contract law and Consumer Protection legislation) but every time I'm put off by getting on a black list at Avis.

My only conclusion is that Avis do this deliberately, and keep it at a small charge so that people will lose the will to fight it.

Clearly now I will only rent with Avis once other options are exhausted.