Get the cleaning recipe, not the cleaned data

Based on the problems we identified, give me the transformations I
should apply. I will apply them myself in Excel.

My tool: [Excel / Google Sheets] and my comfort level: [formulas only /
comfortable with Power Query / can use scripts]
How often I do this: [one-off / monthly / weekly]

For each problem give me:
PROBLEM - restated in one line
FIX - the exact formula or the exact Power Query steps, ready to paste
WHERE - which column to put it in, and whether it should be a new
  column rather than overwriting
CHECK - how I verify the fix worked, as a specific count or comparison
  I can run (e.g. "row count before and after must match")
RISK - what this fix could damage if my data has a case you have not
  seen

Rules:
- Always fix into a NEW column. Never overwrite source data.
- For possible duplicate entities, give me a PROPOSED merge list with
  a confidence level for each, for me to approve. Do not merge
  anything automatically.
- If I said this is monthly, prefer Power Query over formulas so the
  steps are saved and repeatable.
- Order the fixes so that earlier ones do not break later ones.