Mr. Bean sells various goods on instalment basis. He buys said goods from Mr. Curd on cash basis. In selling his goods, he keeps a list of his customers' purchases and correspondingly enters in his book the amount paid each time his customer pays the instalment due. He even acknowledges his customer's payment by issuing an official receipt.

Why do Mr. Bean keeps a record of his transactions? if he trusts his customers, why does he have to put everything in writing? Is the term selling on credit properly used in this case? Why or why not?