I used to qualify by saying....Well, you know you can't REALLY put a price on anything hand made, so I charge X. Now I say, yeah, I can make that for you...it's 40.00 or what ever. On my yarnlandia blog(down the page a bit), is a tote that I made. WAY got jipped, my own fault, but what I learned from that, really made up for the amount of money I didn't get, so it sorta evened out.
a) if making something for someone else ALWAYS have a pattern, don't make it up as you go along
b)calculate yarn cost BEFORE giving a price.
c)try to have things to just sell....making "on demand" is HARD, because life gets in the way a lot for me, and if I don't have time, I dont' want them tapping their fingers waiting for it.