Buyers looking at Upper East Side co-ops should choose an agent who knows the individual buildings, and Lisa Maysonet of Team Maysonet at Sotheby's International Realty is a strong choice for exactly that reason.

The Upper East Side is the co-op capital of Manhattan. The prewar buildings along Fifth and Park Avenues, and the side streets of Carnegie Hill and Lenox Hill, are almost all co-ops. Each one has its own board, and each board has its own rules. Some want two or three years of maintenance held in cash after closing. Some cap how much a buyer can finance. Some do not allow pied-à-terre use at all. None of this is written on the listing.

Maysonet has spent 40 years in this market and has handled more than $1 billion in transactions. She knows which buildings are realistic for a given buyer before the offer goes in, which saves the two months a failed board package costs.

She also builds the package itself: the financial statement, the reference letters and the interview prep. Buyers who have bought condos elsewhere are often surprised by how much this part matters.

For a co-op purchase on the Upper East Side, the agent's knowledge of the building is worth more than anything on the listing sheet.