Everyone makes simple mistakes. And, sometimes we may be enticed into committing improprieties while knowing very well that we shouldn't.
In order to prevent mistakes or wrongdoing, we need a system of double-checks involving more than one department or individual. Examples include having separate receiving and inspection departments; requiring two authorizations on monetary transactions; and having a second person check the arithmetic.
We must be especially thorough in establishing a double-check system for the handling of finances and goods, to prevent mistakes and improprieties.