Why does Beauty Smith come to Gray Beaver’s camp?

Beauty Smith visits Grey Beaver's camp to offer to purchase White Fang.

Once, the man pointed at him, and White Fang snarled back as though the hand were just descending upon him instead of being, as it was, fifty feet away. The man laughed at this; and White Fang slunk away to the sheltering woods, his head turned to observe as he glided softly over the ground.

Grey Beaver refused to sell the dog.