The trick I find for sanding PLA, PETG and ABS is to do wet and in stages. Dry creating melting friction as does not do the job well. Cool running water starting with 280 Drywall screen, 320 wet, 400 wet, 600 wet, 800 wet, 1000, wet, 1500, wet, 2000 wet and then can polish 3000. if it small pieces a multi surface nail file work great. I have a GP38-2 G scale 1:32 and looks injection molded. It took a while but well worth it.
