For me, I usually craft for free, but mention that I take tips. Normally, people tip really well and then sometimes I get very little, but it all balances out, imo. I also always keep the dust unless the person asks for it.
Spells definitely shouldn't be free. If that person doesn't want to spend their time getting a crafter up to high levels then why should they get things handed to them? I don't expect a jeweler to give me free jewelery because I didn't level one up. The money at the end is the reward for working hard to get to the top and I think crafters deserve it. (Although I guess that is a biased opinion since I'm an 80 sage and who doesn't want plat?!

)