Maybe offer small boxes as well as medium boxes by color or type (kids, brights, Christmas, etc.). Give approximate yardage (10 - 12 yards) and approximate lengths (1 - 3 yard pieces). I'd be will to risk $20 - $25 for a grab bag box color of my choice. Once people hear comments back from others about what a good deal it is, their doubts will vanish or the grab bag idea just isn't for them! Good Luck