As a former NYC area realtor and long time resident, you need to know that NYC real estate agents are ruthless, aggressive, back stabbing liars. It's the wild wild west so to speak. Even though I left because it was costing me more money than I was making, I was starting to become one of them which I did not intend to happen. So..
To answer your question, the seller's agent is representing the seller. The agent can work with the buyer in a dual agency role BUT in NYC - never let this happen to you. You need to learn that the seller's agent will do everything to get you to pay the highest price and have the best terms that are good for the seller - not you. They know every trick to undercut you.
You need a buyer's agent to represent you only. However, you want a buyers agent who has recently sold or listed homes in the neighborhood that you are buying in. Do NOT get a buyers agent who sold 5 homes in Brooklyn or Manhattan and nothing in Queens. You need to ask your agent to show you the FULL LISTING sheets that prove the homes were sold by your agent. Your agent's name should be listed as "Selling Agent" or Buyers Agent" If your agent refuses, find somebody else. It means your agent just lied to you.
Also make sure your agent will do everything to fight hard to make sure you get the best deal. You don't want your agent to be scared of the listing agent.