Should i take my car to a shop?

Last week my car was rear ended. The sound of the impact was horrible, but thankfully the rear bumper had little damage. something some paint can fix. The car is drivable. However i do not know if there any damage under the car. The person who hit me had an ins adjuster come look at my car. Of course he could not look under and told me i am to get my car fixed cheap and wrote up an estimate. the ins person is not somebody who works on cars and frankly i think i should take it to a collision repair shop. The ins company says i HAVE to go by their estimate. any truth to this? thanks