Opportunity usually knocks when least expected.

For those in the workplace, that knock may come in the form of a headhunter’s phone call. And, contrary to what may seem logical, it’s often those not actively in the job market who are targeted first.

So how do you make sure you’re not hanging up on your next career move? Experts offer the following advice about building a good recruiter relationship.

Understand why you’re being contacted

If you're happy at your job and aren't looking for a new one, it may seem odd that a recruiter is calling you. But think again. According to the experts, those qualities make you exactly the type of candidate a headhunter is looking for.

"Recruiters and executive searchers are always after the people who are gainfully employed or happy in their jobs. Otherwise, with the help of the Internet, recruiters are simply an online career service,” said Wendy Murphy, a managing partner at C-suite level executive search firm Heidrick & Struggles. “Remember, this is ‘search' not ‘find.’”

And recruiters are creative in identifying potential candidates, especially when it comes to using the Internet. Headhunters can now access your job history through professional social networking sites and blogs. They are also trained to maximize Google and Yahoo searches, said Jeanne Sturges, editor of monthly industry periodical Executive Recruiter News.

Realize where they’re coming from

There is often a perception that headhunters are just trying to get jobs filled quickly, without much regard for who fills them. A vice president at a big financial services firm in New York (who asked not to be identified because she remains in contact with recruiters) said the headhunter that helped her get her current job was good about sending her relevant leads, but that she’s worked with others who mismatched her entirely.

“Some [recruiters] are just throwing stuff at the wall and seeing if it sticks,” she said. “These are not the type of people you want to work with.”

What’s all the rush about? Well, some recruiters need to fill jobs to get paid. 

There are typically two kinds of recruiters: retained and contingency. In simple terms, retained recruiters are paid regardless of whether they fill positions, while contingency recruiters are paid only when they place someone. Though both types of recruiters have an obligation to the employers that hire them to find quality workers, recruiters who work on contingency may be more inclined to push jobs on the wrong people just to make a placement and get their fee, experts said.

Still, good headhunters--retained or contingency--should make the effort to get to know the people they seek out.

“Whenever possible, we like to meet our candidates. A resume only tells you so much,” said Richard Vickers, a managing director at recruitment consultancy Michael Page International.

Be honest

The best advice is to be truthful when dealing with a headhunter, especially when discussing job history and compensation.

“Honesty and transparency make the whole process a lot easier,” said Murphy at Heidrick & Struggles. “It’s ok to have been fired – people get fired for various reasons. Just be honest,” she said.

A major responsibility of job recruiters is negotiating salaries on behalf of the employees they're trying to place, so providing a recruiter with accurate information is critical. And accuracy is taken seriously: At Murphy’s firm, recruiters now require W-2 forms as proof of job candidates’ current income.

Make the most of it

It’s important to remember that job seekers have no financial obligation to headhunters, whose pay comes directly from the employer that hired them. Therefore, job candidates should not feel pressured to accept a job just because a headhunter offers one, said Debra Wheatman, manager of career and admission services at Vault, a career information Web site.

Even if no job comes of it, a headhunter can be a valuable resource in showing someone the job opportunities available, and also in providing skill-building insight. A good recruiter will follow up after sending a candidate on an interview and use that feedback to offer honest, constructive advice – whether or not the placement is even made, said Vickers at Michael Page International.

Stay in touch

Your relationship with a headhunter doesn’t have to end once you’ve snagged the job of your dreams. The financial services vice president mentioned earlier, for instance, admits to staying in touch with several recruiters who send her job pitches constantly.

According to the experts, it’s all about building and developing long-term relationships.

“Establishing trust takes time,” said Wheatman of Vault. “Sometimes those relationships can last a whole career.”