A couple of times, I found myself in a situation where I'm just opening a position and haven't hired developers in this particular stack and this particular skill level for a while, I may not even know what's a current market rate for this position would be. I'd get an overall idea after talking to 5-10 candidates, estimating their skill level and listening to what's their asking price is.

It's not even about trying to low-ball someone. Low-balling might be good in short-term, but not in long-term - both from perspective of a manager who's trying to do best by the company (because you want to build trust with your employees), and from a perspective of a political manipulator (when you inflate salaries of people you manage and budget of your department, you become more important in the hierarchy - saving company money won't earn you as much political points). What it is about is simply not having enough information about the market.