Hi:
I booked a car through AutoEurope for my trip to Croatia and Slovenia. AutoEurope confirmed that the Sixt office in downtown Zagreb had confirmed the availability of the car so I paid for the rental, and showed up in Zagreb with the paid voucher.
Sixt's Zagreb office said they had no car available for me and said they had never informed AutoEurope of any availability. In fact, they said AutoEurope had never contacted them! I was thoroughly shattered since I had not planned for this scenario. But the Sixt agent was very helpful and he called a different car rental company (Uniline: http://www.uniline.hr/croatia/car_rental_croatia.php) and asked them to send a car. He also asked them to honor the rate that I paid to AutoEurope.
All in all, the Sixt agent came to my rescue, and I could complete the rest of the vacation as planned. BTW, AutoEurope did refund me the money, but I don't think I'll be using them ever again.
Thanks,
D