I had booked a car for three days (paid 110 euros), at caldera (caldera.com.gr) agent in Athens, Greece. After two hours waiting in the queue because the owner didn't have the cars on site (he was bringing the cars himself from all over around Athens), we were informed that they couldn't give as the car because they needed a credit card to hold 900 euros for guarantee. We offered to pay cash instead but they rejected!
I emailed rentalcars and they responded that they wouldn't cancel the order, since I had to notify them 3 days before the pickup date! What's the point? If I knew I wouldn't get the car I wouldn't have booked it at the first place.
Finally rentalcars paid the owner with my money, I got no car, and no refund!