The expensive sprays is just to add a white matt surface to the object, you can use whatever you like, even hairspray is great to make the object matt.
those expensive sprays lets you wipe it off without any residue left http://3dprintboard.com/images/smilies/smile.png
if you scan an object with light and dark areas there will be a surface (scale) difference in the final scan,
so it's better to make the object one solid colour or tone down the difference between the dark and lighter parts.
Scanning geometric smooth objects is not easy, because the software has no reference where one part ends and the next scan part begins, it needs a reference,
a trick it to stick small black dots in a random pattern on the surface and inside to let to software see those reference points.
Attachment 9380