Why? How are honest values more "noisy" than faked ones? I mean if it turns out that more programmers work in places that have San Francisco salaries, then those values will dominate anyway. If people in other smaller cities with lower salaries artificially inflate theres for the survey, they survey will present a skewed result. If they enter the correct values, then whatever information can be extracted from it will also be more accurate.

I recommend people don't enter "adjusted" information in.