(MONEY Magazine) - A recruiter calls, or an old colleague pops up out of the blue, and the next thing you know, an exploratory lunch becomes a job offer. Thing is, you haven't really decided to leave--and you suspect that, played carefully, the offer will translate into bargaining power with your current employer.

Just know that fishing for a counteroffer can be risky. For one thing, the outcome is far from certain. Most employers do make counteroffers, but only rarely: The majority do so less than 5% of the time.

Here's how to play your cards right.

• Don't bluff. If you have no intention of taking the new gig, don't pretend otherwise. Your bluff may be called. But you can still use the offer to your advantage. Just make it clear that it was unsolicited and that you're not interested--but that you'd like to use its terms as a jumping-off point for discussing your future.

• Know what you want. Assuming that the new offer holds genuine appeal, think hard about what would improve your current gig enough to make you stay. Nothing less than a promotion or raise? Or would more responsibility, a more interesting assignment or a flexible schedule do it?

• Step gingerly. Even if you're willing to walk, don't alienate your boss--and possibly cut off negotiations before they start--by playing hardball. Approach the conversation in a non-threatening way. "Say, 'I have another opportunity, and I'd like your advice on figuring out what's best for me,'" says Steve Gross, a compensation expert at Mercer Human Resources.

• Control the damage. If you accept a counteroffer and stay, the balance of power shifts back to your employer. You may have gotten a raise or promotion, but more will be expected of you, your loyalty will be in question, and your escape hatch is probably gone. Redouble your efforts, just as you would if you were on a probationary period in a new job.