Financing a co-op can pose special financial challenges. Some boards require a 30 to 50 percent down payment and allow financing for the balance, while others don’t. Every board is different and the practices differ depending on the area.

For instance, when Anita sold her small New York co-op apartment that she had lived in for four years and moved to the West Coast, she had only enough money from her sale to afford a condo or co-op, rather than the three or four bedroom, two bath house she had hoped for. After a month of house shopping, she finally found a co-op that she could put 50 percent down on to keep her payments low and filled out the application.

A couple of days later she got word that the board had accepted her offer. ‘‘It was amazing,’’ Anita said. ‘‘When I bought my New York coop the board ran a credit check, employment check, and called my references. Here in San Francisco the board seems almost indifferent, and the financing was up to me, with no minimum down required.’’

Like condo and townhouses, co-ops can be a good investment if you do your homework and buy wisely. A knowledgeable agent who knows the market and the buildings is the best way to start. This is a niche market, and you want to find an agent who knows the co-ops. In New York City, for example, there are real estate brokers who specialize, not just in co-ops but in specific buildings and neighborhoods.

They know the market and the board preferences, so they can help you assess your possibilities of getting past their requirements. They also know the gossip on the buildings—on their maintenance reputations, code violations, and resident turnover.