ERA The Norton Group
When you walk in, tell the agent that you are working with a buyer's broker. If the agent makes a fuss about the commission, walk out.
Call you agent. He or she can make an appointment for you at a time most inconvenient to the listing broker.
If his/her mother never taught him/her to share, you are not going to. There is no point in confrontation.
As a buyer broker myself, I've always felt most comfortable emailing the listing broker to tell them that I am sending over a buyer of mine. That way it is documented in writing that I have a relationship with the buyer. If the other broker makes a big deal out of it, tell them that I won't send my buyer, and will set up another time to come look at the house. The listing broker would probably always just rather have the buyer come to the open house, as it saves them an extra trip to come meet you at another time.