[eluser]obiron2[/eluser]
Normally when renting a car, you would not pay for it on the website (you may still need to validate the credit card)
When you collect the car, you would pay the up-front rental costs, a deposit and the rental company may 'test' the card for further payments in case you are late returning it.
So I would say that no a shopping cart that takes payment is not required, however you would still need an order basket to let the rental company know what sort of car and extras the customer is expecting to receive.
Obiron