Import CSV or text files

I have three vendor CSVs exported from different systems that need to be combined. Import each CSV into its own sheet, ensure dates import as YYYY-MM-DD, trim any leading or trailing spaces on text fields, and append them into a new sheet named Combined Vendors. On Combined Vendors, add a Source column showing the original filename and run a quick duplicate-row check, then save a backup copy before any edits.

Before I hand the merged vendor file to procurement, make the import auditable and easy to reconcile: normalize the vendor names to the procurement master where possible, highlight rows with unparsable dates or amounts, surface the total spend per source file at the top, and add a short note listing the files imported and the exact time and user who did the import.

I imported three vendor CSVs and the totals are wildly larger than expected; only me and the procurement lead will see this. I suspect a decimal or thousand-separator mismatch from different exports but I can’t tell which file or column caused it. What targeted checks should I run to locate the mis-parsed file and fix the numeric formats safely so I can re-import without breaking other fields?

Every time I import external CSVs I spend 30–90 minutes fixing date formats, trimming spaces, and reconciling vendor name variants. This repeat work eats into analysis time. What one habit or small automation step should I introduce so future imports arrive clean enough that I only need to verify, not repair? Give a practical first action I can implement in the next two days.