The court would rule in sue's favor because courts seldom inquire into the adequacy of consideration.
In contracts, consideration just means the exchange of things of value. There has to be an exchange of things of value for there to be an enforceable contract, and in this case a watch was exchanged for money. It is rare for courts to rule on how much consideration is expected because people are generally free to set their own prices and not sell if the price is too low. That is not for a court to decide (in most cases).