They could easily do that, or thought they could, by making life at the ranch unbearable for him.

That, he was convinced, was the reason that Betty had adopted her cold, severe, and contemptuous attitude toward him.

She expected he would find her nagging and bossing intolerable, that he would leave in a rage and allow her and Taggart to come into possession of the property.

Neither she nor Taggart would dare make off with the money and the idol as long as he was at the ranch, for they would fear his vengeance.
He thought his manner had already forced Betty to give him his father's letters and admit the existence of the idol--she had been afraid to lie to him about them.

And so Betty was "stringing" him along, as Taggart had suggested, until he completed the repairs on the buildings, until he had the ranch in such shape that it might be worked, and then at the end of the year Betty would tell him that his reformation had not been accomplished, and she and Taggart would take legal possession.
But if that was their plan they were mistaken in their man.