You must be wise, but not too wise.

You must never actually cheat the customer, even if you can. You must make her happy and satisfied, so she will come back.

You will deal with ignorant, opinionated and innocent people. You will often have an opportunity to cheat them. If they could, they would cheat you, or force you to sell at less than cost. You must be wise, but not too wise. You must never actually cheat the customer, even if you can. You must make her happy and satisfied, so she will come back.