Many of us tend to think of personal income as a private matter. A person's worth isn't determined by how much he or she makes - so why should a prospective employer think otherwise? Some job seekers, though, get an unpleasant surprise when an interviewer pops the question of previous salaries - and it's important to know how to respond in a way that preserves your negotiating position without compromising your shot at the job. Understanding why some employers ask this question can help you provide an answer that keeps you safe on both those fronts. Here's how to approach your response.