Get a broker to represent you. I know that in some States a buyer pays to have a buyers broker represent them, that isn't the case in New York. Buyers commission is already included in the price, and if you go there on your own the seller can't exactly suddenly go from 6% to 3%. That's a law suit waiting to happen between broker and seller.
Get a broker, he'll do the research, he'll show you comps, he'll advice you on an offer to submit, he'll qualify you, find you an attorney if you don't already have one, can tell you about the building and everything else. Pass that headache to someone who gets paid for it, and leave it off of your plate, it will be a smoother ride for you.
Btw, where are you buying?