They come from BMA with the bushing already installed in the arm. Your mechanic is probably thinking that you ordered them separately in which case he is correct. When you receive them, show them to him and he will probably be ok with it. Remember he is not making any money off your parts when you order from BMA. Some places charge extra for installing "customer parts" because the profit on parts and labor is factored into keeping the shop open.
If you are handy, you can change these yourself. It helps a lot to have a lift and it should be about 1.5 to 2.0 hours of shop time.
Mike Holbrook