I make many commissioned quilts, always with a deposit to cover the cost of the materials -- fabric, batting, thread, and extras, up front.
I also use a contract signed by both of us, stating the object to be made, the design, the quilting design, the fabrics and batting to be used, the approximate length of time the work will take, and when the final amount will be paid before the quilt is delivered.
Years and years ago I was told by a business owner/mentor: "Business is business and friendship is bulls---." I knew what he meant, not in a bad way, and have tried to conduct most business decisions under this premise since.
Jan in VA