There are additional problems with using debit cards when renting cars. Some car rental companies do not accept debit cards. Some, sepecially these outside of the US, do really high 'authorization holds' - in Australia there was $2000 such hold that usually equals to the deductable (they call it 'excess'). If the account does not have such amount it will cause other set of problems to the cardholder, like overdraft, etc.