“For you and me, it’s too good to be true,” he said. “For the guy who has been working in the oil fields, how is he supposed to know?”

Of course, fraud and just plain bad advice are not limited to the poor or unsophisticated. Robert P. Rittereiser, the former chief financial officer of Merrill Lynch and former chief executive of E. F. Hutton, is working as the receiver for two funds suing J. Ezra Merkin, a former money manager who steered money to Mr. Madoff. Mr. Rittereiser did not think investors in Mr. Merkin’s funds knew that their money was simply being passed on to Mr. Madoff. But even if they did, they may not have seen anything to be concerned about.

“They were investing money and getting appropriate returns for the kind of fund it was,” Mr. Rittereiser said. “Most of them had a relationship of some kind and confidence with Merkin and the people he was dealing with.”

So how do you protect yourself? The first step would seem to be picking an honest adviser. The good news is that only about 7 percent of advisers have disciplinary records, said Nicholas W. Stuller, president and chief executive of AdviceIQ, a company that evaluates advisers. The bad news is that those violations appear only after someone has filed a complaint.

Mr. Stuller’s company, which has now approved some 2,400 advisers, rejects anyone with any type of infraction — from a securities fine to a misdemeanor for getting into a fight. He said this policy might keep some good advisers off the site, but his goal is to search the records of federal and state regulators to find advisers he knows are clean.

“There are advisers who have significant negative disciplinary history with one regulator but appear to be pristine with another regulator,” Mr. Stuller said. “There was a guy in Minnesota who was stealing insurance premiums. In his enforcement record, it says, ‘We’re going to alert Finra,’ but his Finra record is clean,” he said, referring to the Financial Industry Regulatory Authority. “That’s where the regulators don’t talk to each other.”

AdviceIQ’s main competitor, BrightScope, takes a different approach. It notes disciplinary actions taken against advisers but leaves it up to the consumer to go to regulators to determine what the violations were.