At first the parties are promisors. During agency they are principal and agent. When the institution buys from the supplier, it is buyer. In the final Murabahah sale, the institution is seller and the client buyer. Deferred payment then creates creditor–debtor status from the sale price.
This rule is especially important in financing because cost-plus sale (مرابحة) is valid only when the financing remains a real sale. The sequence of ownership, possession, risk and final sale must therefore be visible in the transaction.