Interview at least three brokers. “You’re the CEO of this transaction, so own it,” said Ms. Braddock, who suggested questions like: Have you sold in my neighborhood? Have you sold in my building? And, in the case of a co-op: Do you know anyone on the board?

Ask what deals they’ve recently made. Ask how long they’ve been in the business — although if someone is a relative newbie, that isn’t necessarily a negative. “Experience is important, but it isn’t the only thing,” said Gary Malin, the president of the residential real estate company CitiHabitats. “If you just focus on a résumé, you may miss out on someone who is really good.” After all, a younger person may be hungrier and more energetic than an elder statesman.

By all means, get references and check them.

Ask for a listing presentation — a pitch that includes data on comparable sales and the specific plan the broker has for marketing your apartment. While you’re at it, ask your top candidates to show you some other properties they’re representing, said Stuart Moss, an associate broker at the Corcoran Group. “And not just the property itself but the whole building,” he said. It will give you a sense of how the brokers will comport themselves when potential buyers come to look at your apartment.

Give a wide berth to the broker who seems to be telling you only what you want to hear, the one who says your apartment is worth far more than the valuation others have placed on it. “I frequently say, ‘Don’t choose somebody to sell your home based on the number he puts in front of you,’ ” Mr. Moss said. “The market determines that, not the broker.”

Similarly, beware the broker who says your property is just perfect as it is. “Because they want the listing and don’t want to offend potential clients, some brokers are afraid to say what work an apartment needs to get it ready for the market,” Ms. Braddock said. “My contention: It’s just the reverse. This is a job interview, and brokers should treat it as such. They should be direct and honest.”

And, said Allison Chiaramonte , a sales agent at Warburg Realty, they should be at least reasonably likable. “Sellers sometimes focus on brokers they perceive to be tough or forceful negotiators,” she said. “But it can turn off the buyers and their representatives if a particular broker has a reputation for being difficult or unreasonable. You’re better off with a team player who gets deals done.”

Buyers

If you’re buying, look for a broker who asks the right questions, among them: What’s your timing? What’s your financial picture? Are you prequalified for a mortgage?