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Are you sure the person you asked to vouch for you isn't actually blowing your shot at a job? Follow these guidelines for getting effective recommendations.

MICHELLE SIMMONS thought she had the job locked up. She had already aced two interviews for the position as a nutrition counselor in the Los Angeles area. All that remained was a reference check. Simmons offered up the name of her supervisor at the assisted-living center where she used to work. After all, the woman had once told Simmons she'd be happy to provide a recommendation. "Based on that and my work history, I didn't think naming her as a reference would be a problem," Simmons says.

After two weeks passed without word, Simmons called to inquire. She was stunned to learn she had not gotten the job. Since this was the second time she'd been turned down by an interested employer, she was suspicious. She hired a firm to call her ex-supervisor, posing as an employer. Though the former boss lauded Simmons's dependability and communication skills, she also said she wouldn't hire her back and that there had been "minor conflicts" between her and management. "I was hurt and upset," says Simmons.

Without a good reference, Simmons, 34, felt she had little chance of finding work in social service. She has returned to school to become a paralegal — though she's not happy about switching careers. "I had my heart set on that job," she says.

It happens more than you might think: The person you pick to sing your praises winds up sabotaging your job prospects. Sometimes it's intentional. But often it's nothing more than an offhand comment meant to balance an otherwise glowing review. So how can you avoid getting burned? Be candid with the people giving references for you, advises Don Teff, an outplacement consultant in New York: "Ask, 'Is there anything negative about me that could show up in a reference?'" And since many employers ask open-ended questions such as "What's the candidate's management style like?" coach your reference on what skills to emphasize.

Start laying the groundwork as soon as you leave a job. Confirm basic information such as dates of employment, positions held, salary and reason for leaving. If a potential employer hears something on a reference check that's different from what you told them, "they might question your truthfulness," cautions Teff.

Just because you don't name a former supervisor as a reference doesn't mean the recruiter won't contact him. If you had a bad experience, call that manager and explain that you'd like him to focus on your positives. If he won't budge, send a letter to your old HR department requesting it limit all references to strictly factual information. "Most employers err on the side of saying too little because they're afraid of getting sued," says Wendy Bliss, a human resources consultant and an attorney in Colorado Springs, Colo.

Not sure you're getting slammed? Some detective work may be in order. Simmons paid $87.95 to use Documented Reference Check (www.badreferences.com). MyReferences.com offers a similar service for $59 to $99 per reference, depending on how thorough you want to get. Discover your old boss mentioned the tequila shots you downed at the Christmas party? A strongly worded letter from a lawyer should put the kibosh on him. For $68.95, Documented Reference Check will fire off an official-looking cease-and-desist letter.

Legal revenge isn't so easy. Lawsuits involving bad references are typically based on defamation of character, and the burden of proof is usually on the employee. Also, most states have statutes that protect employers if they give "truthful, good-faith references." Translation: A former supervisor can call you a slacker as long as he had good reason to think it was true.

When you're the one giving a reference, you also have to be cautious so that you don't wind up undermining the candidate unintentionally. Think of it as a court deposition. Be brief, and answer only what you've been asked. Spontaneous remarks are often what get people in trouble. It's okay to bow out of a reference request if company rules prohibit providing one, but be careful not to raise suspicion. "Say, 'My company has an incredibly stringent policy, but there's no inference to be made that there's anything wrong with this person,'" suggests Gary Kaplan, an executive recruiter in Pasadena, Calif.

Of course, there may be times you feel obligated to point out negatives about a candidate. How can you protect yourself legally? While defamation law varies by state, there are some general guidelines for staying out of trouble: You're safe if the information is true (even better if it's documented), job-related and shared in response to specific questions, and if the person receiving it has a legitimate need to know, says attorney Bliss. Steer clear of such comments as "He's good for a 50-year-old," or anything else that relates to age, race or religion. "That could be used by employees in a discrimination suit," says New York attorney Katharine Parker.

Another no-no: Passing off rumor as fact. When project manager Kenneth Stanbury applied for a Washington, D.C., construction job, the company called his former employer, Sigal Construction. An executive there said Stanbury "seemed detail-oriented to the point of losing sight of the big picture." After Stanbury lost the job, he sued Sigal. During the trial, the exec admitted that his impressions came from hearing people talk at "casual luncheons" and "over a beer on a Friday afternoon." That alone wouldn't have been a problem, but he had failed to mention that he had never worked with Stanbury, even though the employer had asked to speak to someone who had. Stanbury was awarded $370,000.