Ahhh... So Avis is doing this across the board.
As an engineer, and a numbers guy I highly doubt that the fuel level measurement systems in Avis' cars meet Minnesota's (or most other states) weights and measurements standards for commerce. If Avis wants to charge their customers an effective rate of $115 per gallon of fuel not returned they should be subject to the same measurement accuracy qualifications and inspections that every gas station in the state is subject to.
What a complete scam...