Never, never surprise a customer. Make sure they know the charge is up front, while the quilt is still in her hands so she can easily walk away with it in case it is more than she wants to spend. You should accept the job with a set percentage down....especially if you have to buy materials such as backing or batting or matching fabric. You are a professional, and are expected to be a great estimator of time required. If you miss calculate, suck it up, and get better at your job. Have an agreement, like dry cleaners, if you don't pick it up and pay within 30 days (?) of done, state what happens to the quilt.. (goes to charity, whatever). If you are offering a discount, state that up front. Make out an order form, fill in some information, estimate, fine print, ......something......, and give her a copy as she leaves. No surprises. You'll get better at this, and you will thrive or quit based on outcomes. But you wont worry, whine, or be disappointed. Best wishes in your endeavor. There are many quilts that need to be repaired, loved, and cherished. It is wonderful that you contribute to this great cause.