A supplier ships goods, invoices, and gets paid. Ninety days later the customer files bankruptcy and a trustee demands the money back. Nothing was wrong with the transaction, the supplier did nothing improper, and the demand is nonetheless well founded. This article explains why bankruptcy treats ordinary payment as a recoverable transfer, what the preference elements actually require, and which defenses do real work. It then covers fraudulent transfers, where the theory is that the debtor gave away value rather than that a creditor received too much, and the safe harbors that immunize enormous categories of payments. It closes with the practical side: how to evaluate a demand letter, what documents decide the case, and the settlement dynamics that resolve almost all of these disputes.