Most accidental marks happen during ordinary handling. A few habits can greatly reduce fingerprints, hairlines and dropped pieces.
Prepare the surface
Work over a clean, soft mat with drinks, food and loose tools moved away. Sit down if possible so a dropped item has less distance to fall.
Hold edges, not faces
Skin oils and salts can leave lasting marks. Handle bare pieces only by the edge. Clean cotton or powder-free nitrile gloves may help, although loose cotton can reduce grip.
Keep capsules closed
If a piece is already protected, avoid opening it without a reason. Wipe the outside of the capsule rather than the metal and use an air blower, not your breath, for loose dust.
Never stack bare collector pieces
Metal-on-metal contact can create fine scratches. Use individual holders and keep enough space in storage so capsules do not grind against each other.