Which of the following can be categorized as income in QuickBooks Online?

Service fees can be categorized as income in QuickBooks Online because they represent revenue earned from providing services to clients or customers. In accounting terms, income is generated from the core business operations, and service fees reflect that by recognizing the payments received for services rendered.

Expense reimbursements, asset sales, and rent expense do not fit the definition of income in the same manner. Expense reimbursements are typically not considered income since they represent money received to cover previously paid expenses. Asset sales can contribute to income but are often classified separately as gains on the sale of assets rather than regular operating income. Rent expense, on the other hand, is a cost incurred by a business and does not generate income at all. Therefore, out of the provided options, service fees are the only choice that directly aligns with income in a business context.