Selling a co-op or condo in New York City is easier than getting a child admitted to preschool here. But it's not the more straightforward exchange of money for property common elsewhere in the country. Multiple blessings are required: By lenders--which must approve the buyer, the apartment and the building before your buyer can get a mortgage--and by neighbors, in the form of co-op and condo board approvals. Even in a seller's market, pricing your apartment too optimistically, or picking the wrong buyer—one who gets rejected by a co-op board or a lender, for instance—can turn your apartment into a pariah and cost you money. Here’s what you need to know.