Put simply the scanner can misread your foot. Without a professional examining and looking at your foot there is a lot of room for mechanical error. My son hopped on it the other day. I was curious so I indulged and watched him. 
He has a flat foot with some issues in the front part of his foot. He has been in our little steps and doing great. The scanner said he had a high arched foot and that he needed very little support and lots of cushion. It suggested the completely wrong orthotic. I feel bad when patients come in having spent $50 and I get to be the bearer of bad news that it was the wrong insert. 
My suggestion... get a full evaluation by a professional and find out what you really need before letting a machine guess and waste your hard earned money! 
Dr. Misty McNeill
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D.P.M. - Founder of Prairie Path Foot and Ankle Clinic