Keep a courteous tone, no matter the circumstances. If you must deny a person credit, discontinue credit, or begin the collection process, maintain a professional tone as you explain your reasons for taking this action. Remember, you'll probably want to keep this customer's business, even if you must ask for cash payments.
If you must deny a request for credit, leave the door open to future applications from the same party.
If payment is more than a month late, encourage the customer to contact you to discuss the lapse in payment.
If a payment is more than 60 days overdue and the customer has shown no move toward making the payment or discussing why he or she has not made payment, let him or her know exactly what the penalty will be unless he or she responds immediately with the payment. Don't make an empty threat, however. You must be prepared to follow through.
Be clear and include enough information to clearly convey your request or offer to your client or potential customer.
Tailor your letter to your audience.
Be brief; letters of credit should be straightforward and businesslike.
Be confident and persuasive. Be assertive but not overbearing.
Assure your reader that any information he or she gives you will remain confidential.