Why did Francois say that buck was worth $1000?

Francois valued Buck at $1,000 due to his exceptional strength, intelligence, and capability as a sled dog. In the harsh environment of the Yukon during the Gold Rush, a dog like Buck, who could pull heavy loads and work efficiently, was seen as invaluable. This high price reflected not only Buck’s physical abilities but also the demand for reliable sled dogs in that era.