[mattm]

The best advice I have received about pricing:

Price your service so that you would not regret it either way.

Before giving a price I usually think of how I will feel if I don't get the job and how I will feel if I get it. If I would be comfortable with both situations, then I know it is the right price regardless of what happens.

In line with this, I have given higher rates to "difficult" people I have worked with before that have asked me to do work for them again. I didn't get those jobs (usually I don't even get a response) but I was happy about it. If the work and person seems interesting, I may quote a lower rate.