1. Using improper sanding paper (too coarse)
2. Sanding before the primer thoroughly dries and continuing to coat
3. Using excessive Thinner.
4. Using the Thinner which evaporates too slowly
1. Use proper sanding paper or one which is extra delicate for the work
2. Sanding once the primer is cured
3. Adjust the viscosity of paint and Thinner properly to suit each coat
1. For few sanding marks, leave the paint thoroughly dry, sand with the sanding paper no. 1500-2000. Sand again with swirl remover.
2. In extreme cases, scrape off the coat, apply the primer and refinish.