If I were you, I'd also make up a paper to give your customers which outlines steps they should take to prepare the quilt top for longarm quilting. Include : top and backing all need to be square, all loose threads on back of quilt top need to be trimmed, etc. It's amazing how many good piecers will come with a lovely top which is just not square. I guess they just don't bother to check for that and measure it in several places once it's finished. And it's important for you to know if it's out of square, and how much, before you tackle it.