Your best recourse is to discuss with an attorney. Keep in mind, however, that if you looked at the property, you did not rely solely on the listing information (which may be considered to have been "believed to be accurate, but not guaranteed"). Quite often in Queens, Brooklyn, and Long Island, unit owners don't know the square footage of the unit. They may guesstimate or go by information that they received over the years (which might not have been accurate). Also, the coop/condo may apportion square footage based in part on gross space including shared areas, such as hallways and elevators (which you might find to be a ridiculous thought, but may factor into how they calculate maintenance/common charges).
Keep in mind also, that you as a purchaser likely had several protections built into the process. These include legal representation to review all coop docs and an appraisal which would show the measurements the appraiser calculated. Also, if you got a mortgage loan, the unit appraised for the value you paid (okay, it is possible for this statement to untrue, but only with borrower knowledge, consent, and additional contribution).
The first thing I would do, if I were you would be to check the appraisal report (if you didn't get one, contact your lender and request it.). If the numbers match the 780sft, then I'd think you really have a weak case. Also, ask yourself where you got the 780 number from (coop docs, appraisal, measuring tape + your own calculations). Make sure you're right before you invest a lot of time, energy, and money into this type of undertaking. I'd also ask myself if I'm happy with the unit (how important was the represention on the paper versus what you saw with your own eyes). Even if the square footage where accurately represented, there's no guarantee that you would have gotten the unit if you offered less. After doing these things, decide whether you want to spend the time, energy, and money to make an issue of this.
Good luck! I hope everything works out for you.
First of all you may have an ethic complaint against the broker. Contact Professional Standards at Long Island Board of Realtors if they are a realtor, 631-661-4800. Ask for Judy Becker and she will forward you the pertinent information.
If the listing information was fraudulent, you may well have legal grounds for recourse. Contact a reputable real estate attorney for advice. Who did the selling broker work for? What did the listing say?
If you need additional information, please feel free to contact me at your earliest convenience at my office in Bayside at 718-279-8762.
Very truly yours,
Douglas Montgomery, Bkr
This is a legal question. Did you have your own Real Estate Lawyer? Was the sq footage in writing and was it approximate? Please contact me by email if you would like a list of reputable NY real estate lawyers