NYC vacation rental market is swamped with blatant scams. It is safer to stick to airbnb.com or roomorama.com when looking for an apartment for short-term stay. Craigslist might still have the best bargains though, if you've got the time and patience to hunt for them. In order to weed out the scams, stick to two simple rules: after you've made contact with the person offering a place for rent, ask the magic question: "With all the scammers out there, could I please send a local friend over to take a look at the place before booking?" (doesn't matter if you really have anyone there who could go over, no reply = scammer). Second, do not pay anyone anything in advance unless there is a way to reverse the transaction (read: PayPal only). Anyone requesting full stay's rent plus a huge deposit in advance via bank transfer or money order is a scammer, and they're most likely using photos and descriptions stolen from legit real estate ads.
Is this your business?
Secondly, since the law change in May 2011, short term apartment rentals are illegal in NYC, and therefore it is very hard to find out what is legal and real, rather than illegal and real, which many many apartment rentals are.
airbnb is a great option, but choose the option of a Private Room, and you'll have a legal apartment, and you'll share with people who already live there. I've done that and it's cool, because you get a locals opinion on places, and get to visit the real NYC.