I, too, use two seperate sets of scales to get my riders to see where they are unbalanced. This also works for international riders (mainly from Asia) who come here for brief periods of time to ride. They've had years of lessons at home, and then they get quite upset when I point out that they're riding unbalanced! But the scales never lie!
I didn't know about this tip until I heard Cristoph Schork explain it at the AERC Convention in Reno last year. What an eye-opener it's been for everyone here since!! Thanks Cristoph!
Another reason that I've found riders rider 'bent' or 'twisted' in the saddle is if they're holding the reins with only one hand. I've got nothing against the rider doing so, however it does tend to twist the body. If you're holding the reins in your left hand only, your left shoulder is generally slightly forward, turning your entire body slightly to the right. If this is how you ride, try holding the reins with both hands equally, and see how your entire body changes balance.
