Definitely a hard lesson for you to learn, but the rest of us will benefit by learning from you. I've only made 2 quilts from scratch on commission. The first was a baby quilt for a friend's granddaughter and she basically only paid for the material, but I knew going into it that she really could not afford to pay what it was worth.
The second one is a Cal-King bedspread...we went together and she bought about $100 worth of the material, gave me $60 for thread and we agreed upon $600-700 for the completed quilt. Well, after extensive piecing and buying quite a bit more material, the top is pieced, not quilted yet. After I showed her a picture of the quilt, she gave me $500 cash and said that when I finished the quilt she would give me another $500...and told me if I had to buy more material for the backing I was to let her know because she didn't think it was fair for me to have to pay for it! THAT'S the kind of friend/customer we all need!!!
From now on, I will ask for 1/2 the price up front, with a contract detailing that the deposit is non-refundable and when payment in full needs to be made or the customer's interest in the quilt is terminated. I never thought to ask a customer whose quilt I am quilting to pay anything up front, but I do know that I won't give back a quilt without getting paid in full.