Why is Karana’s father suspicious of Captain Orlov and the Aleuts?

Karana's father knows that the Aleuts have caught 105 bales of otter, but Captain Orlov offers him only one trunk of beads and iron spearheads. Negotiating, the chief demands three more trunks, and Captain Orlov promises to bring them from the ship after packing up the pelts. To protect the tribe from being cheated, Chowig insists that they leave behind half the pelts until they have paid in full.