Did Hertz try to scam me?

I rented a car with Hertz in Germany, from May 1st until May 4th, through rentalcars.com.

Companies make mistakes. When you double the number of companies involved the chances of a mistake go up. That is because there was one contract between you and rental.com, and another between rental.com and Hertz; but the interaction when you picked up and dropped off the car was with the people at the rental car location.

On the day that I got the car, May 1st, Hertz charged my debit card 981$.

I thought this was a deposit hold and didn't think much of it.

In my experience if there a deposit it is mentioned at the time of the reservation, and when the car is picked up. It is also on the pickup paperwork.

However, when the amount wasn't unblocked after two weeks, I realized it was an actual charge.

When you drop off the car, they give you a receipt showing all the charges, so the total that would be pulled from the bank account should have been clear.

I then went through my emails and saw that I had received a bill on May 4th, the last day of my rental, that claimed that I had driven 3000 more miles than the allowed 900 miles, at .33$ per mile. I had of course not driven that much...

I have to assume that either you didn't check the receipt, or you did a drop-off that doesn't interact with the staff.

...called Hertz who agreed that the amount was wrong, claimed that the mileage was misrecorded at the time of renting, refunded most of the charge, and sent me a new bill with the corrected mileage.

I am glad it worked out, it could have been even tougher because you could have been required to argue with rentalcars.com.

Is this all just a weird way to structure deposits on debit cards within their billing system? Would they have refunded the amount without my input? The employee that I spoke to didn't sound so

Maybe. You have to look at all the paperwork, from both companies. No they never would have recalculated the bill because the computer generated it based on the data into the system.

There are actually more charges, for 21$ in both bills (for damage and theft waivers that I explicitly refused) that I'm currently still trying to get refunded, and all of this just seems very sketchy.

In my experience the insurance related charges are hard to change after the car has been picked up. Again the paperwork has to be reviewed.

Note: In the past debit cards could not be used to rent a car, then it was changed to be possible but there were large security deposits. Now they seem to be accepted at more companies. The nature of the debit card transaction still does make the movement of money more complex.