If I take out a library book, and they charge me $.10 per each additional day extra.
Or if I owe money on a bill, and they charge me a $10 late fee for being overdue.
Are these a case of Ribbis? Or is there something that differentiates these two cases from the typical: Reuven borrows $10 from Shimon, and pays back $11?
(assuming both a Jewish library, and Jewish company)