"What is the role of an insurance agent in the US?"

I use two agents for different types of policies. What they do is send out to different companies what you want in coverage and they get back to you with the best price and policy. By using two agents you can also play one against the other.
Now my parents like Allstate and that is a separate office that just sells Allstate. Never had a problem with them.

Now to start a new subject in the same thread. In NJ we use Public Adjusters to settle claims for you. They represent you for a fee and deal with the insurance claims department. I know on the West Coast they never heard of such a thing as far as I know.

Barry