>In the article the author says we should use "pre-approved vendor lists" or "streamlined approvals" and that sounds great in principle, but could also easily be exploited.

As patio11 would say, "The optimal amount of fraud is non-zero". Fraud is bad, but if fighting fraud involves so much red tape that it costs more than whatever petty corruption could ever cost, it's bad.

[1] https://www.bitsaboutmoney.com/archive/optimal-amount-of-fra...