I am not the lowest price in town nor am I the highest (although I am closer to the higher cost then the lower).
If someone refuses to even pay the service call charge, I dont argue with them, I'll try and reason but its not worth the headache. I think most people are good by nature and will keep to their word.
I understand it could be tough to get someone to agree to the service call charge, but even if you make it $xx it still lets you know you will not be wasting your time, energy and gas for some prie shopper who wasnt giving you the job anyway.
I guess my original point was that you know the homeowner isnt going to be 100% honest with you about whats entailed with the job and without seeing it, you could never give an accurate price.
Good luck, and if you need help implementing it let me know if I could help.