You can test yourself. On a flat section, ski straight down the hill on one foot, then the other foot. Is it easy to go straight (good), or do you need to move your body around to go straight (indicates the need for alignment). Repeat 45° to the right of the fall line and 45° to the left of the fall line. You should be able to go straight on one foot without moving your body around.
You can test yourself at home, maybe with a mirror or with a helper. Wearing shorts and your boots, are the centers of your kneecaps directly above the centers of your feet, and do they stay centered as you flex up & down? Check the center line with a plumb bob hanging down from the center of your knee, or a carpenter's square with the short side flat on the floor. If your position has your knees coming together, you need cants with the wide side on the inside of the feet, and vice versa for the bowlegged person. Alignment can be corrected with wedges (cants) under the bindings, or grinding one side of the boot sole, or wedge shaped add-on boot soles or the sole wear inserts. http://www.bootech.net/pages/why_alignment.html
There's also alignment of the ankle. You can test this. Stand with your feet angled so when you flex your knees, your knees track parallel, not inward nor outward. Look at your feet. If your feet are splayed outward, you're pronating (me). If your feet are pointed inward (pigeon toed), you're supinating (my friend, John). Stand with the insides of your feet parallel. Flex your knees. Do your knees come together (pronating) or move outward (supinating). Posted footbeds that raise the inside of the foot for the pronators and the outside of the foot for the supinators are the answer to get your ankles aligned. (Here's the cheap way to give it a try, and I don't know if these work in ski boots...look for a Dr. Scholl's Custom Fit Orthotics device in a Walmart.)