Which expense is write-off related to non-payment by customers?

The correct answer is bad debt because it specifically pertains to amounts that a business has recognized as being uncollectible from customers who have failed to pay their invoices. When a company sells goods or services on credit, it may occasionally encounter situations where customers are unable to pay due to financial difficulties or other reasons. In these cases, the company must account for these uncollectible debts by writing them off as bad debt, which directly impacts their profit and loss statement.

Bad debt is accounted for as an expense, which reduces the overall profit of the business, reflecting the impact of these non-payments accurately in the financial statements. This option is essential for portraying a realistic view of the company's financial health and ensuring that income is not overstated.

The other choices do not relate to non-payment by customers. Discounts allowed refer to reductions given to customers as an incentive for early payment or as a promotional strategy. Bank fees are charges that banks impose for account management and other services, not related to customer payments. Shop rent and utilities like electricity are fixed costs that the business incurs regardless of customer payments, and thus they do not directly reflect issues of non-payment by customers.