I think the only solution is to check the fabric while you are at the cutting station and if it is NOT straight, then hand it back to them to give you a new fresh cut of fabric. They won't be making those mistakes too much longer. Owners won't be happy to have all those 'remnant pieces' at discounted prices cuz their staff won't cut straight.
I haven't done that exactly, but I have taken fabric back to Joann's when the cut was bad and they did replace the fabric. It was just a pain in the butt for me time wise and having to drive and use the extra gas.
my 2 cents
warm quilt hugs, sue in CA