From: How to Answer the Question "What Was Your Last Salary?"
No one is going to overvalue your services, but plenty of people will undervalue them. You have to value them first, and valuing yourself includes knowing when to say "I'm not comfortable with that request."
When you find your voice, your muscles grow. When you cave and cower and pretend that going along with any off-the-wall request or demand is the safe -- and therefore best -- option, your flame will shrink.