Had a prepaid (booked directly with Sixt through the Android app) PCAR booked at LAX but only offered a Camry or a Jeep Grand Cherokee (SFAR as we found out) offered and everything else was a paid upgrade. There were other vehicles (Corvette, BMW 440) but they wouldn't give us anything else. Claimed other vehicles were vans, etc. Asked the agent and she refused to budge.