Most "bad file" tickets I get are a first-layer problem.

If it's an Ender (or any bed-slinger):

• Wash the bed with dish soap, not IPA as the first move. Grease from fingers beats "I leveled it."

• Set Z-offset so the line squish looks like a flattened ribbon, not a round noodle.

• First layer: 20–25 mm/s. Fancy speeds come later.

If it's a Bambu:

• Don't fight the stock profile on day one. Dry filament. PLA that sat open for a week will look like a bad model.

• If the skirt is patchy, run the live Z tweak during the first layer — not after the print is 40% done.

If it's a Prusa:

• Live-adjust Z while the first layer is down. If you only leveled cold, you didn't level.

• Textured PEI wants a slightly hotter bed than smooth PEI. 5°C is often the whole fix.

The file can be perfect and still fail if the first 0.2 mm is wrong. Fix the bed before you re-slice the model.

When the machine itself is the problem — clog, layer shift, crashed firmware — that's a live session, not a forum thread.