How does it usually work with agent's fees if I walk past a building in Manhattan and see a sign saying "apartments available, contact xyz realty", would they still charge me the fee for "finding" the apartment for me?
Yes. You will still have to pay a broker's fee which usually amounts to one month's rent. It is definently harder to find a no-fee apt but it can be done. Your best bet would probably be craigslist. Good Luck!