I've done alterations for the general public for over 40 years!
(yikes.. that's a looooooong time)
And figure if I can't earn at least $10 per hour, I'm in the wrong business. In this part of the world, people that clean houses earn that much. Honestly, that doesn't require as much skill as repairing an heirloom quilt.
Believe it's important to give the customer an estimate and while doing that inform them it's not "written in stone", as you never know what you're going to run into.
Know the value of your work!