An import needs a target object, a field map, a mode, and an identity strategy. Insert creates records, update changes existing matches, and upsert does either according to a stable matching key. A row number or display name is usually a poor rerun key.
Inspect the source before running it. Trim incidental spaces, normalize fields only when the business treats them as equivalent, and keep required values present. Reconcile inserted, updated, and rejected counts with the input rows. Partial success means some records may already exist, so repeating an insert can make a bad load worse. An upsert should be repeatable without creating another copy of the same external record. Assignment-rule invocation is also an explicit import decision.