Who is the designer and who is the sales?!

When a car was built at the factory and sold by a dealership, what do you call the person who sold the car? the sales, duh! Well, so how come an employer who does not know any interior design who can hire a person doing all of the design work but the employer still can declair him/herself as the interior designer? Well, why can't we call the employer an interior design sales, or maybe we should start to call the car dealership's sales automobile designers?!