If an involved party claims that a Bill was only of this type of Bill, and the transaction never occurred: Ketuvot 19a
If a signed Witness claims that a Bill was only of this type of Bill, and the transaction never occurred: Ketuvot 19a-b
For the Creditor to invalidate this Bill, where he is a debtor to another and therefore is indirectly hurting his creditor: Ketuvot 19a
Prohibiton against keeping such a Bill around, because of its Danger: Ketuvot 19a-b