When people call me I give them my hourly rate and inform them of my service fee. I also assure them that I will be able to find and fix the problem in a timely manner versus a cheaper less experienced handyman. If they don't want to pay then thats too bad, they don't get my services. Don't give your work for free, also you may want to charge something like a service fee or hourly minimum for the service call that took you 45 minutes to drive to just to find a light bulb not screwed in all the way.
