Who should take the measurements and mold for an orthotic?

In our opinion, only someone who is a trained professional who knows how to take the measurements and the mold by placing your foot in an optimally corrected position.  Utilizing a correct technique you end up with a corrective orthotic and not just one that approximates the length and width of your foot as with the supermarket and drugstore type "scanners" as described above. 
Furthermore, this trained professional will follow up with you to ensure you are getting the maximum benefits from the orthotics.  Only a trained professional knows how to evaluate the orthotics and make appropriate modifications or adjustments if the need arises.