Most 'bad STL' tickets are a wet spool
I keep getting the same message: "this file won't print." Nine times out of ten the file is fine. The spool isn't.
PETG left open for a week strings like crazy, first layers look like cottage cheese, and people blame the model. PLA is more forgiving until humidity hits ~60%. Then you get under-extrusion that looks like a bad mesh.
Quick check before you rewrite your slicer profile:
Weigh the spool. Compare to the dry weight on the label. A jump of 10–20g is water.
Print a 20 mm cube with the same filament. If that fails, it's not the STL.
Dry 4–6 hours at the filament's spec. Reprint the same file, same orientation.
If the cube is clean and the model still fails, then look at overhangs, wall count, and orientation. Not before.
Machines that won't home, skip layers, or throw firmware errors are a different job. That's a live session, not a file tweak.