There are a few tell tale signs that will indicate if you are or are not working with the right agent:

1. First and foremost, the agent should listen to you and understand your needs very clearly. A bit of skepticism is warranted if words like 'My exclusive on 78th street would be perfect for you' are uttered within the first 30 seconds of your initial conversation with a real estate agent. Until your agent has thoroughly discussed your needs with you, it is impossible for him or her to suggest that any apartment would be perfect for you, much less one of their exclusives.
2. Your agent must have comprehensive, current knowledge of the narrow sub-market that you are interested in. If you feel like you know more about the market than your real estate agent does, run and run quickly and far. Unfortunately, because many buyers are referred to aunt Susie's hairdresser's best friend's brother-in-law, this happens more often than you may think. For example, if you are looking for a two bedroom loft in Tribeca, your real estate agent should know that market like the back of his or her hand. He or she should know virtually every loft building in Tribeca and should have visited in the past two weeks at least a dozen apartments that are comparable to what you are looking for. If you feel like your real estate agent needs a subway map to find out how to get to Tribeca, then that agent is probably not the right one for you.
3. Your real estate agent should act as an advisor, not someone who will simply show you apartments. Anyone can show you an apartment - this does not take much expertise and thus should not be thought of as your real estate agent's primary purpose. Rather, once your agent has a firm understanding of what you are looking for, he or she should provide you with current information about the sub-market of interest to you (i.e. what is on the market, what apartments are selling for vis a vis their asking price, how quickly apartments are selling, what is the demand like vis a vis supply, how has inventory increased or decreased recently, how realistic is the pricing of a specific apartment, what are the board requirements of a specific building, etc.). Quite simply, your real estate agent should be an expert in what you are looking for and you should not settle for anything less. You do not want someone to become educated in the market on your time.