There are a lot of qualities that can be mentioned here, to determine what makes a good mortgage broker. Like most of these questions, context is important.
Above all, the sign of a good mortgage broker, is the mortgage broker who listens to you and tries to understand your goals, and your needs. A good broker, also takes the time to explain his or her role, and set expectations.
A good broker will be direct with you, never beat around the bush. The role of the broker is to advise you after getting a good understanding of your situation, and comparing that to your demographics.
At the end of the day, you, as the clients, are always calling the shots. We as mortgage brokers are there to help provide you with everything that you need to make an informed decision.
There are others, however these are the top signs of a good mortgage broker.