Usually, they give you what they have available at the time. 2 weeks ago I rented a car at the San Francisco airport. They gave me a choice between a Hyundai Sonata and a Chevy Impala.
do car rental companies give you the car that they advertise in the picture?
not always the same car in the advertisement. They often do this to bring you in the shoot you out the door in a beater. You can call and see what models and years of the car they offer. Depends on the area what you might end up with.