Most “bad STL” posts I see are not bad files. They are a first layer that never got a fair chance.

Three tells:

The skirt looks chewed. Nozzle is too low. Raise Z a hair before you touch flow or temp.

The first layer is shiny in patches and matte in others. That is usually a dirty bed or a fingerprint, not the model.

It printed fine yesterday. Filament picked up moisture overnight, especially PETG. Dry the spool before you reprint the same file at a new temp.

I keep a small calibration pack for this exact rabbit hole, plus a separate 1-hour live fix if you would rather screenshare the machine. Files and the hour are not bundled on purpose. Mixing them makes people think they bought support forever.

If you post a first-layer photo, include printer, nozzle size, and bed temp. That trio solves more than another slicer profile.