More often then not folks renting cars are in a hurry. For instance, your plane just landed and your luggage is waiting, etc., so you do not read all that fine print in the contract and, of course, the fine customer service rep working with you has likely been trained to only say things that might maximize revenue. What happens next?
Well, Dan Gillmor tells us

about a man who was charged more than $3,000 for a car rental because he took the car out of state without realizing that would violate his contract. How did Payless, the rental company, know? It was using satellite-assisted tracking equipment to spy on the customer.

The original article is here.
The charge of $1/mile for driving outside the state of origin is surely excessive. I do not even understand the logic of the charge. And it is not nationally common. Example, fly into Cincinnati I mean Kentucky to go to Cincinnati. I have done this quite a few times and not been charged anything extra.
Sure, the guy should have read the contract. But I argue that failure to disclose and explain potential extra charges in big print on the front page may be deceptive given the context of the typical rental transaction.
And, the Oregon proposal (mentioned in the comments) to use GPS to calculate your driving miles as a basis for taxes is just broken before it gets out the door.