Answer:
In order to understand how important ethics are for some company positions, we can pretend to be the purchasing manager of UPS and we must buy 10,000 trucks and vans for our delivery fleet. This purchase will be worth more than $300 million easily and that means a huge sales commission and a huge profit for the company that closes the sale.
Imagine that we are reviewing the specs of 2 or 3 different proposals and someone from a car company, e.g. GM or Ford, decides to visit us and makes an offer of $1 million if we accept their proposal.
What should we do? Any unethical person would clearly just grab the money and close the deal. Who could blame them, that amount would change someone's life. But is that decision ethical? Probably not.
If you accept the money, you would actually be receiving a bribe, which is not only unethical, it is also illegal. Ethics is basically our moral compass that guides us into doing what we consider right, and should help us to not do things that we consider to be wrong.
Ethics are not the same for all of us, some people might consider that it is more important to improve your family's well-being, than the well-being of the company. That is why ethics and morality provides us with some guidelines and general rules about what is right or wrong. Certain positions in a company are extremely sensitive to corruption, and purchasing is one of the most sensitive ones and not only for large purchases, but also for more common and everyday purchases.