Corrupted special characters
The export comes in a different encoding than the import expects, and half the names end up with symbols instead of letters. It is noticed two weeks later, when someone searches for a client and cannot find them.
Conversion to the correct encoding happens when the file is read, before any matching.
The doubled database
The import is run twice, because the first time it “did not work”. Now the database has every client twice, and reports show double.
Matches with existing records are shown before the import, not after.
The flattened pipeline
All leads go into the first stage, with no value and no probability, because the import did not know what to do with those columns. The sales forecast becomes useless.
Stage, value, probability and source have their own fields on import.