deceptive switch to higher rental fee

I rented a car through carrental.com with Enterpise picking the car up at Dulles Airport near Washington DC.  When I got to the Enterprise counter I was told I rented a car in Chantilly, VA (no idea where that is).  If  I wanted to rent from the airport location I would have pay more for the rental.  Easy solution for me, I won't use carrental.com ever again.