I, too, often don't care for the commission quilts I have to make. I ask for a potion of the cost up front, "So that I can purchase the fabrics and supplies". This also covers my patootie if the 'buyer' reneges on the finished quilt. Then I am at least not out the cost of the thing they aren't going to get. (If I really don't want it then, I donate it to our guild's community quilts project.)
I photocopy the check and tape it up where I can see it during the piecing and quilting. This keeps me focused on the result for me....more payment at the end! Or, sometimes, I post a page out of a catalog of some fabric, book, tools I'm looking forward to buying.
Jan in VA