i think that it will be next to impossible to find a hire car company anywhere, let alone Crete, that will agree to hiring you a car without either taking a credit card no or a sizeable cash deposit. Your best bet is going to be either to take out a card or protect your deposit as carefully as possible by

a) Going over the car with fine tooth comb before accepting it and making a complete list of every little scrape, scratch and defect and getting this list agreed and signed by a company employee.

b) Take photos of any existing damage with a digital camera that will record time and place they were taken.

c) Never ever go off metalled roads - not easy in Crete in you want to explore the mountain areas or even get to some villas.

d) When returning the car make sure that you return it with the same amount of fuel in it as it was provided with.

e) Leave yourself plenty of time for the same minute inspection of it and again get a company employee to sign this off as a definitive list of bodywork damage. This could still leave you open to claims re mechanical damage so you might want to even insist that they take it for quick trip around the car park too.

SM