When the allowance method is used to account for uncollectable accounts, bad debts espense is debted when?

a customers account becomes past due, an account becomes bad and is written off, a sale is made, or management estimates the amount of uncollectable?

Also, which is not a principle of sound accounts receivable management?

Determine a payment period, determine to whom to extend credit, delay cash receipts from receivables if necessary, or monitor collections?