A Buyers broker will try to negotiate a best price and hopefully some if not all of the transfer taxes the developer will dump on you which would be detailed in the Purchase Agreement. Perhaps even more. Usually, a developer will also try to dump his Attorney costs on a buyer. You will probably be required to contribute some amount of the common charges as a new development needs to start their reserve fund. The broker who will represent your interests will get paid by the seller's side as this is a co-broke sale.
You'll know they represent you because the NY State Dept of State requires an "Agency Agreement" form to be explained and signed by you which will detail what party is represented by which broker. As for where to find such a buyers broker, that shouldn't be difficult. I might suspect you have family, friends or co-workers who could recommend someone they have used before. I wish you all the best.
To answer your question regarding the incentive for a buyer's agent. Well they are not working for free. The agent will be paid either from the commission already offered to the buyer's agent or deduct their commission from your offer but from my experience usually the former is in place. Buyer agents will typically work with you in a more relational capacity as oppose to transactional allowing a more rewarding experience for you while working in your best interest. In return they are looking for your referrals and will treat them the same. The agent will most likely be able to recommend an attorney,and loan specialist and even the home inspector. When your "team" is on the same page, it facilitates a more harmonious experience because purchasing real estate today can be a daunting experience.
Back to your original question. a buyer's agent will help you through the process and any possible red flags, we are not privy to the building you are considering.
You need both. The agent has all the listings on the market and is going to help you find a home at no cost to you. When you sign the contract and at the closing you need to have a lawyer. The agent can not give you legal advice it is not qualified for that.
Veronika Baba Kian Realty NYC