Plastics can become electro-statically charged which attracts dust. To prevent static charging, you can wipe the material with special antistatic cleaning agents. The dust-repellent effect remains for a long period of time.
If you don’t have an antistatic cleaning agent, you can easily clean acrylic or Plexiglas with a soft lint-free cloth with a little washing-up liquid or you can use a slightly damp micro-fibre cloth.
If there is a scratch, it can easily be removed from the smooth surface. First treat the scratched area with wet sandpaper (grit 240), and then regrind it using fine sandpaper (grit 400 or 600). Finally polish the surface with a soft cloth and standard car polish or polishing wax again.