Scanimate

Is it true that we wash the materials before scanning?
Yes, unless the materials are delivered in an unopened new box or if you want to keep the dirt for visual effect.
You can see how dirt and dust are visible on the gloss map. The top image is unwashed material, the second is wiped with a damp cloth, the bottom is washed with special chemicals and wiped with microfiber using microfiber gloves.
If the material is not washed, all the dirt and stains will be visible, as shown in the attached render. (We do not remove scratches, they will remain.)

A good, informative discussion at California State University, East Bay