So are you saying that a Corolla was the largest car that Budget had available when the car was reserved? If so, that's unfortunate, but it could also happen with other rental-car companies. Some locations even sell out completely at times.

Will your employer permit you to rent from a different company when Budget does not have a full-size (or some other type of car) available for higher-level employees? If you have a need for a larger or fancier vehicle for client interaction, I should think that your employer would carve out an exception when Budget does not have the type of vehicle you need on a particular trip.