An owner of the advertising firm has a close friend working as the top manager in the mobile company. As a result of the friend's assistance, the advertising firm was able to win the bidding contract for the exclusive advertisement of the new mobile phone design. In return, the friend was compensated in cash for his help. Which of the following options cannot prevent this fraud?
1) Disputing inappropriate items with vendors
2) Establishing strong controls over the vendor master files
3) Determining the support for payments to the vendors before recording a liability
4) Conducting background checks as part of the employment process