"You can provide a lot of value-add to clients by giving them the lay of the land before they move abroad," he says.

Some advisors feel it's necessary to turn to outside experts for help with expat clients. "I'm foundationally knowledgeable, but I try to find professionals who've developed a niche in this area," Morris says. She adds that roughly one-fourth of her clients are expats who went abroad for work-related reasons.

She says it's comparable in her regular practice to finding tax advisors and other professionals with niches in estate planning or other areas that aren't her fortes. "There's so much involved with all of these [expat-related] issues," Morris says. "Each country is different because you have to look at tax treaties and other issues within each country."

Morris says one place she goes for help is the Cross-Border Planning Alliance, a group of five advisory firms with specialties in cross-border financial advice. The group includes Wruk and Rodriguez, along with a certified financial planner in India.

"Advisors should find someone to assist them in this area," says Wruk, an Alberta native who's also a registered advisor in Canada. "All of these top people you might have lined up here in the U.S.--estate planning attorneys, accountants or investment managers--are totally irrelevant when you move to a foreign jurisdiction.

"If a client is moving to the U.K., you need someone who's an expert in U.K.-U.S. tax treaties," he continues. "If you manage money for someone who's going to reside in the U.K. you have to ask what securities regulations you might be violating because you're not registered to manage money over there. Even though the money is located here, you're providing investment advice to a resident of another country, and you can't do that without being registered there."

One thing to consider, says Wruk, is whether E&O insurance coverage applies to advice provided to someone residing in a foreign country.

Anja Luesink, a New York City-based certified financial planner, believes that most advisors can adequately handle expat clients on their own if they create the right network and don't extend themselves to jurisdictions beyond their knowledge and comfort zone.

Luesink has a number of foreign national clients from her native Holland who live in the U.S. "I try to attract clients from there because I'm aware of their circumstances," she says. She also has foreign national clients from Canada and Great Britain. She says she's built a network of specialists in those countries, such as tax advisors who are familiar with local tax issues.

"I wouldn't take on clients in places I'm not familiar with, such as Mexico," Luesink says. "You have to be very careful or you'll make mistakes. But who else will do it? You have to start somewhere to build expertise."