You know generally what's paid for your position, and so does the employer. What they also know – and you may not – is what they can afford to pay, though chances are it will be the market norm. Not everyone can or will negotiate.

Some people's natural tendency is to up the ante when stating the amount expected. Be cautious about this, because you don't want to be seen as someone who over values his/her skills (i.e., someone who is arrogant, rather than confident) or is totally mercenary (even if you are).

So when you answer, let the employer know what you discovered in your salary research, do a brief sales job about your excellent qualifications and experience, and sum up by stating what you expect to earn based on these factors. Doing anything else will waste their time and your time.