This is from a recent Hertz rental in Europe
NO SHOWS/ LOST RENTALS
If you pre-paid, fail to cancel your reservation and do not collect the vehicle on the pick up date, we reserve the right to make a No Show / Lost Rental Charge of EUR 95.00 (or local equivalent - see below) which recovers our administration costs and compensates the Hertz company providing your rental for their inability to rent the vehicle when it was reserved for your use.
In this case we will refund your prepayment, less the No Show/Lost Rental Charge, if you write to us within 90 days of the pick up date at Hertz Prepaid Accounting Department, Hertz Europe Service Centre, Swords Business Park, Swords, Co. Dublin, Ireland requesting repayment and enclosing a copy of your Reservation Confirmation.
If you pay at location, fail to cancel your reservation and do not collect the vehicle on the pick up date, we reserve the right to make a No Show / Lost Rental Charge of EUR 65.00, GBP 65.00 (or the equivalent in the destination currency, exclusive of VAT) which recovers our administration costs. This will be taken from the credit card you used to make your booking.
I was once a "no show" on a 1 day pre-paid rental, I was not charged anything more than what I already paid for the rental (was about 45€)