A good broker can save you time and trouble. Because brokers have advanced access to more available apartments, they can help you land a better deal than if you search on your own. The tradeoff is price. Paying a fee equal to 8 to 15 percent of a full year's lease can alter what you can afford. No one likes that.
The apartment a renter eventually decides on is generally not the one he or she first inquired about. More often, it is one the broker matched to the renter's needs and expectations. So again, find and work with a broker (or brokers) you feel you can trust.
Is the broker showing you apartments that match your stated needs? Is the broker helpful in describing the neighborhood, the rental building, the transportation concerns, the noise issues, etc.? If your broker is experienced, he or she will be full of useful information. If not, that broker isn't the right one for you.