Some secrets have to do with accounts that advisors don't know about.
Prior to starting his own fee-only financial planning firm, Daniel Wrenne, a CFP, was a broker with Northwestern Mutual. One of his clients had a $50,000 investment account with him. When Wrenne let his clients know that he was going fee-only, the man said, "I never told you this, but I have another brokerage account." That account, held with his father's broker, had $1.1 million in it.
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After probing, Wrenne, whose new firm is called Wrenne Financial Planning, learned that because of his commission-based structure, the client worried that Wrenne would pressure him to move the money over to him. Though the client isn't moving the bigger account over, Wrenne will be able to monitor it now.
Then there are the secrets about business deals gone bad. Another client of Wrenne's had gone into a gym franchise with a fellow doctor. A year into working with him, Wrenne found out the client had already lost $50,000 on the venture and he was worried that the deal would become a financial sinkhole that required more money.
"I find out about these things when they go bad," Wrenne said.
—By Ilana Polyak, special to CNBC.com