Is a purchase valid if an agent is instructed to buy a slave for one hundred and buys one worth less than one hundred?

Primary text

The purchase is not valid if the agent buys a slave whose actual value is less than the stipulated one hundred, even if the purchase price was lower. This is because the agent contravened the order and did not achieve the principal's intended objective (acquiring a slave of that specific value, i.e., worth one hundred), even if the purchase price was lower than the instruction.