Middle managers are learning what executives have known for years: Hiring an expert adviser during job negotiations often brings you better pay and perks.

Pay coaches, lawyers and compensation consultants increasingly sell their negotiation expertise to employees below the highest rungs of the corporate ladder. But while such counselors can help you sweeten your job package, their advice doesn't come cheap. So with everyone from self-help authors to academics writing books on how to bargain for better pay, when does it make sense to shell out a lot of bucks for a personal pay specialist?

Here are answers to some basic questions about how the industry works.

What do they do?

A pay adviser's job is normally twofold. First, they research average salaries and total compensation for a specific position. Depending on how much detail a client wants, they can dig up what people in similar positions earn nationally, locally or even at a particular company. They compare total compensation, including bonuses, vacation days, health benefits, commissions, stock options or whatever else is of interest. Mostly they use published salary data from the Bureau of Labor Statistics, private human-resources firms and trade-group research. Also, since most consultants get the bulk of their business by helping companies set up equitable compensation plans, they often have independent data. If need be, they call experts in the particular field to collect more compensation data.

Second, they advise individual clients on how to improve their negotiating skills. They'll coach you on strategies such as what to say -- or what not to say -- and how to thwart common curveballs that hiring managers throw. One typical example is how much you earned at your last job, says Lee E. Miller, a Morristown, N.J., negotiation expert and author of the book "Get More Money on Your Next Job." Instead of revealing specifics about your pay, redirect the conversation toward your skills and what else you offer to the company, Mr. Miller says.

"The minute you give them your [previous] compensation, it kind of determines what you're going to get." Mr. Miller suggests requesting that the manager make an offer before discussing previous pay.

A personal pay consultant also might engage in role-playing to make a client more confident before negotiating. Mr. Miller once coached a young woman by sitting next to her while she talked on the phone with a prospective employer. He says consultants can help people practice asking for things and find creative ways to negotiate for nontraditional perks the company might grant, such as getting a workstation set up at home. "I've seen people get things simply because they ask for them," he says.

Unlike lawyers, who help clients sort through employment contracts and often get intensely involved with bargaining, most consultants stay behind the scenes and offer only prepping and strategy advice.

Negotiation experts say it's usually unwise to even let employers know you've sought the advice of a consultant, unless it's part of your bargaining strategy. Rather than introduce a third party into the negotiations, it's better for the employer to feel like they're dealing directly, and exclusively, with you.

There is no stigma attached to using a pay coach, says Brian Foley, a compensation consultant in White Plains, N.Y., "but I wouldn't necessarily go out and tell everybody I'm doing it."

Why would you need one?

Reasons can vary. If an employee is a strong self-advocate, knows his or her worth in the job market and feels comfortable negotiating, hiring a compensation adviser may not be necessary.

But someone who's moving into a new position, re-entering a career or simply interested in what others in his or her field earn may retain a consultant to help find competitive compensation data. "There are situations where the base salary is ridiculously low at a competitive standpoint," says Dave Theobold, founder of NetShare.com, a Novato, Calif., online database of job postings for executive positions.

A job hunter who's nervous about negotiating also may want a coach. Even someone who works for a company that's having serious financial troubles may want help negotiating a fair severance package before the company falls apart.

Women particularly may benefit from negotiation practice, says Deborah M. Kolb, a management professor at the all-female Simmons School of Management in Boston. Women are less likely than men to negotiate for higher salaries or better packages, Ms. Kolb says, partly because managers are generally less receptive to their requests.

"A lot of the time it's easier to say no to women," says Ms. Kolb, who teaches seminars to women on better negotiating. In a manager's mind, she says, a woman's traditional split responsibilities -- mother and worker -- can cast doubt on her "ability to produce results."

How much do they cost?

Most consultants charge $200 to $400 an hour, and the bill can easily run into the thousands with complex jobs.

Some consultants charge individuals on a tiered system based on the position, making it easier for lower-level employees to get consultation. Dan Moynihan, a principal at Compensation Resources Inc., a consulting firm in Upper Saddle River, N.J., says his company typically charges CEOs $3,000 to $10,000, while a company treasurer may pay $1,000. For a lower-level manager, the charge might be $300 to $500.

The lower the position, the less there is to negotiate, though. And as Jim Fox, a consultant in Minneapolis who charges $295 an hour, puts it, for someone with little to bargain about "to pay me $200 to $2,000 is, to be honest, basically a waste of their money."

Is there a cheaper alternative?

Pay coaches can dig up precise salary and compensation information that's tailored specifically to your intended job and area, sometimes using their personal knowledge of the company. But not everyone wants to -- or can -- shell out thousands of dollars for that service. Some Web sites now give similar, though not usually as reliable, salary and compensation comparison data.

If you just want to know how much others in your field are earning, you can download reports from such sites as Salary.com or SalaryExpert.com, a site owned by compensation specialists Baker, Thomsen Associates Insurance Services Inc., Newport Beach, Calif. Salary.com, based in Needham, Mass., offers a free database of reports on more than 6,000 positions at all different levels and fields. For each position, the site gives a low-, middle- and high-range salary, along with a total compensation comparison.

For greater detail, the sites sell more personalized reports with more specifics about pay in a particular region for about $30 to $70.

But use information from Web sites with caution. It's important to know where the site gets its information and how old it is. Web sites often make it difficult to find out how old data are or what sources and methods they use to compile it.

Bill Coleman, senior vice president of Salary.com, says one frequent mistake users make is downloading a profile for a position or rank beyond their qualifications. "You need to read the job description and need to be intellectually honest with what you do," he says.

To get cheap, if not better, negotiating advice, try finding a mentor at the company you're dealing with. Such a person is often more effective than a pay adviser, simply because they have inside information and connections. If that's not possible, try an acquaintance outside the company who knows the field or knows negotiating well enough to assist you in learning finesse while you bargain.