When working out quotes or estimates, l tend to spend quite a lot of time getting it right. Not everyone does. I know the figure is right, so i dont get into haggling.
If i cant fine tune it to suit their budget, then i just politely walk away. I usually say something like... "I'm not the cheapest around, but .........." It does help to give people confidence.
If it's an estimate, then i do give a maximun figure that I will stick to if ive got it wrong.