Many samples of business letters of refusal are available at the WriteExpress website. The site offers examples of refusal letters for a wide variety of occasions, including declining an appointment, declining a job offer or promotion and declining a request for credit.
According to WriteExpress, a refusal letter should be as diplomatic as possible and open with a sincere expression of regret and a statement of what exactly is being refused. The letter should explain the reasons for refusal, offering substantive evidence to support the writer's position. It may also offer alternative solutions to the recipient as a consolation. The letter should end by expressing a wish for the recipient's success.