What control activities typically ensure that the occurrence, authorization, and completeness assertions are met for a purchase transaction?

Occurrence:

• Observe and evaluate proper segregation of duties.
• Test of a sample of vouchers for the presence of an authorized purchase order and receiving report
• Review and test entity procedures for accounting for numerical sequence of receiving reports and vouchers
• Examine paid vouchers and supporting documents for indication of cancellation.
  Authorization:
• Review entity's dollar limits authorization for acquisitions.
• Examine purchase requisitions or purchase orders for approval
• Review entity's competitive bidding procedures.
  Completeness:
• Review and test entity's procedures for accounting for numerical sequence of purchase orders, receiving report, and vouchers
• Trace a sample of receiving reports to their respective vendor invoices and vouchers.
• Trace a sample of vouchers to the purchases journal.