Hard Surface Guide:
realistic scuffs, paint damage + weathering

Start by duplicating the subtools you want to weather. Inflate them slightly using the deformation palette.

Then dynamesh the new subtool.

The reason for this is because the mesh might not have polygons spread across it equally, so dynameshing resolves this!

Use a combination of brushes to chisel away at the mesh to reveal the one underneath.

I use Crack Orb brush pack - get it for free here!

Weather down the hard edges. Use the layer brush to add some complexity and give the appearance of chipped-away paint.

With the sculpting done, now it's time to enhance the damage!

This can be done a number of ways, but using the Masking Palette is the best way to go about it.

I generally add a dark shade of color to the cracks making them look more intense.

Once you've finished, decimate the mesh. This will improve ZBrush's performance, and it'll be lighter when you decide to export it into Marmoset Toolbag, or similar.