How many of you charge for estimates and what is a average charge?

My problem is that people seem to be taking advantage of free estimates. The last job estimate I was called for was a city inspection on a rental house which turned up the outside outlets were not GFCI. The owner was told that they needed a permit to change the outlets to GFCI by the city. I looked at the job and the meet with the inspector. We both agreed that this was considered maintenance and didn't require a permit. I called the home owner and informed them of what the inspector said. They were happy with this and we set a work date. The next day I get a message "Since we didn't need a permit my brother took care of the work, so we don't need you, but thanks any way." Now what about the time I lost on another job that I pulled off to meet these people in the middle of the day? Do they think we all just sit around and twiddle our thumbs?
Thanks for any advice.
Don