Financial institutions will have different lending guidelines for condos. Usually a miminum of 51% of the units must be sold before they will lend.
Developers will rent or rent or offer rent with option to buy for units that remain unsold. Some examples of this can be found on Emmons Avenue in Sheepshead Bay.
Bonnie Chernin & David Rogoff
Coldwell Banker Mid Plaza Real Estate
if he cant sell then the condo developer can rent them out until he market improves. This will be common place in overbuilt area like Williamsburg, Brooklyn. The developers specing on the $1000 a sq/ft "luxury" construction and now proud owners of "luxury" rental units.