If the person reserved the car and has not yet picked it up, it's important for them to know, that unless they are using a guaranteed make/model reservation (ie. Hertz Prestige class), all they have is a reservation for a luxury car.
They could receive a Town Car, STS, DTS, 300 (don't get me started on a 300 in a luxury selection but they have shown up at Thrifty/Dollar), etc. Alamo lists a DTS as an example, but their fleet includes many other makes/models of cars in this class.