An over-incentivized sales manager falsifies sales by creating and approving fictitious customer sales orders, which are then processed and shipped prior to year-end according to the clients normal control procedures, which your firm tested and found to be effective. Which of the following audit procedures would most likely detect this fraud?

Vouching accounts receivable to sales invoices, shipping documents, and approved customer purchase orders.

Confirmation of balances with customers.

Examining evidence of credit approval for a sample of recorded sales invoices.

Re-performance of client estimates of bad debt expense using independent estimates.