The answer is:
by providing supporting evidence of a prince believed to be clever because he chose a good servant.
In the excerpt from "The Prince," the author makes reference to the reasons why the Prince of Sienna, Pandolfo Petrucci, has appointed a servant like Messer Antonio da Venafro. For example, he mentions that Petrucci must be intelligent and perceptive enough to identify the good and bad in his servant. As a result, he compliments and disciplines his servant so that the latter remains reliable and does not betray him.