I am a Longarm Quilter. I would not keep any trimmings from a customers quilt, BUT:
If your backing fabric was not cut straight and square your quilter may have needed to trim it to square it up. You can't load it if the top and bottom edges are not straight and parallel to each other. If you did there would be uneven tension on the fabric.
I also try to load the top closer to the top edge of the backing so there is more of a safety net at the bottom. This may have accounted for the single trimming she did return,it would have come from the bottom.
Also remember that the finished dimension of the quilt will be less than the original dimensions. The quilting alone can cause the dimensions to 'shrink' a few %. This effect would be equal in the top and back but if you just measured the backing before and after the quilting you should expect to see a few inches 'disappear.
Most importantly talk to your quilter. He or she wants you to be satisfied with the results.
Last edited by patricej; 11-30-2012 at 08:06 AM.