Clean a list without losing meaningful differences
Decide what counts as a duplicate before deleting rows.
Start with the purpose of the list
A mailing list, a product catalog and a set of source-code lines do not have the same cleanup rules. Spaces at the ends of copied names are often accidental, while spaces inside a product code may be meaningful. Uppercase and lowercase can distinguish file paths or identifiers. Keep the untouched original in a separate file and work on a copy in the editor.
Apply one operation at a time
In this sample the first row has surrounding spaces, the second repeats the same spelling and the third uses uppercase. First preview trimming. Then preview duplicate removal and verify whether the third row remains. Do not assume a case-sensitive rule when you have already lowercased everything. Removing blank lines is a separate decision: a blank row might separate groups rather than represent missing data.
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betaReview the change, not just the row count
A smaller file does not prove that cleanup was correct. Inspect the first and last rows, representative duplicates and any non-Latin names. Copy or download the result only after comparing the preview with your intended rule. If the result is surprising, undo the operation and change one setting. For CSV with quoted multiline fields, use a CSV parser instead of treating every physical line as a complete record.