CSV import should be strict or flexible?

Strict validation과 flexible preview의 tradeoff를 묻는 질문.

CSV import has a real tension: strict validation protects data, but flexible import helps users with messy files. A product that guesses too much can corrupt records. A product that rejects every alias or date format feels unusable. One compromise is flexible preview but strict commit: guess and explain during preview, but block destructive or ambiguous writes. Where would you draw the line for customer, inventory, or billing imports?