Thats correct, for example Thrifty say this about Debit Cards:- At the time of rental, an authorized hold will be secured on your credit/debit card provided to cover the estimated rental charges and any additional charges that may be incurred. These funds will not be available for your use for the duration of the rental. We will place an authorization amount of $200 for a Major Credit Card and $500 for a Debit Check Card.