Actually, the new Fannie Mae and Freddie Mac guidelines have very recently changed and a building where the sponsor owns more than 30% will not be approved by a major lender that follows these guidelines. This doesn't only apply to new conversions. I have a current deal at Ruppert-Yorkville Towers on 3rd Ave. and 91st Street, which has been a condo for many years now and buyers never had a problem buying there. My buyer was recently turned down because the sponsor still owns 33%. Until very recently it was 50% and she would have been fine. Yes, you could run into a problem. Similarly I have a listing at 20 Pine St. in the Financial District and since the new regulations went into effect, I was holding my breath waiting for it to get to 70% sold. Fortunately now we have a deal and it is 80% sold (or in contract, which counts). See if there is sponsor financing or find out if they have a particular arrangement with a lender. You definitely want a mortgage contingency in your contract just to make sure you don't lose your deposit if you can't get financing.