More than three-quarters of home buyers and sellers now begin their research online, experts say, but the key question remains: How do you choose an agent — especially in a competitive place like Manhattan?

“Even though it’s an Internet age, the real estate business is…a very personal transaction,” says Ruth McCoy, executive vice president and managing director of sales, Brown Harris Stevens. “You need a broker who knows the difference between apartments, who’s going to get the best price, who understands both sides of the transaction. Who’s going to shepherd you through?”

The NYC market also presents some distinctive challenges, notes Steven James, senior executive vice president and director of sales for Prudential Douglas Elliman Real Estate. Unlike most parts of the country, Manhattan does not have a Multiple Listing Service so that consumers can see what’s advertised, and may not be aware of many closely guarded listings, particularly in co-ops, which still account for “65 percent of the real estate sales in Manhattan,” James says. “Sellers don’t want unlimited traffic; they rely on the broker to bring in only qualified traffic…You really want a broker who can make that transaction happen.”

While many consumers start their search for agents through referrals, McCoy suggests also checking newspaper ads and real estate firm web sites. “Read the broker profiles,” she says. If you’re a seller, ask yourself, “Who is advertising properties like mine?” McCoy says. “Look at the web site — that will give you a sense of how your property is going to look [in the firm’s listing].”

Whether buying or selling, nothing is more important than meeting brokers before making your choice. “Take the responsibility of interviewing several agents before you make the final selection,” says real estate expert Ilyce R.Glink in her book, 100 Questions Every First-time Home Buyer Should Ask. “If you simply take a friend’s or relative’s suggestion, you may find yourself working with the wrong broker, looking in the wrong neighborhoods, and touring homes that are too expensive.”

Comprehensive knowledge of the current market is essential for any agent. “Today’s market — not yesterday’s or tomorrow’s,” stresses McCoy. Ask agents how they keep abreast of the marketplace, she says. “You want someone who has experience in your building, your area, your type of transaction. And you want your broker to aware of the entire city,” because you may be looking for certain amenities, not just a particular location.

If you’re a seller, invite potential brokers to present a marketing plan, McCoy says. Ask them, “How is my listing going to be displayed? In print? On the internet?” Also ask them to justify the listing price with a range of comps. Find out what an agent’s track record is: “Do they have a handful of deals under their belt?” James says. And, he adds, for buyers in particular, it’s critical that the agent be a good listener. Ask yourself, “Are they listening to what I want, or ignoring that and showing me what they want to show?”

Because co-op sales often involve complex and sensitive transactions, including co-op board approvals, it’s important that your agent get along with a host of potential players. “See how they deal with colleagues, co-brokers, doormen, managing agents,” James says. “Do they get along with them? How they talk to them? Remember, they represent you out there.”

In addition, co-op buyers should make sure their agent can manage the “paper process,” including the financial statements and letters of recommendations. Does an agent address questions asked and collect the data in a professional manner? “You need to make the paperwork look really, really good [to a co-op board],” James says. “Otherwise, a person may not get in.”

For sellers, the issue of commissions remains an issue, particularly in high-priced markets like Manhattan. “There is some flexibility” in the negotiating commissions, James says, although most sellers seem willing to pay commissions in the traditional 5-percent-to-6-percent range. “They see the value in the service. They recognize the importance of brokers.”

Still, when discussing the commission, McCoy advises sellers to ask brokers to detail what specific services they will provide. “It’s so much more than getting the best price,” McCoy says. “There’s a lot to it.” In the end, she adds, “We’re only going to be paid if we’re successful. We can do a great job, but if we don’t do a really great job, you’re not going to close the sale.”

The Agent Interview You can find out a lot about agents just by the way they answer your questions. “If they bristle and seem reluctant to share information with you, that may be a sign of things to come,” says real estate author and columnist Ilyce Glink. Here are some questions you should ask any agent, whether you’re buying or selling:

1. How long have you been in the real estate business, and how long have you been with your current company?

2. How many homes have you listed and sold, especially in the last six months?

3. How do you keep informed and up-to-date about changing market trends?

4. How often do you plan to communicate with me — by phone, e-mail, fax? And will I be working with you directly or with an assistant?

5. What kinds of experiences do you have buying and selling in the price range, the buildings, and neighborhoods that I’m interested in?

6. What’s your marketing plan to reach consumers who fit my niche?

7. What services, exactly, do I get for the commission?