Mr. Harthouse gets along well with Bounderby and the other "Hard Fact" fellows with his easy flattery, and begins to make headway in gaining Louisa's favor without her even realizing it. He "accidentally" comes across her while she is walking alone in the country, and deftly manipulating her feelings for her brother and their mutual knowledge of his ungratefulness for all she's done for him, he pledges to try and help Tom out for Louisa's sake. Louisa discourages him as soon as his compliments start becoming improper, but Harthouse is such a good flatterer that he is able to instantly move away to other topics, only to return in a roundabout manner to professing his admiration for her for the way she cares for her brother. In this way, he begins to establish the beginnings of an intimate relationship with Louisa.
Suave James Harthouse is able to take advantage of Louisa so easily because no one in her life and education of facts has ever showed any awareness of or sensitivity to her own feelings, no one has ever been affectionate to her, no one has ever noticed her unhappiness. Her heart is starved for love, and she is happy, in this moment, to receive even a tiny bit of care and admiration from Mr. Harthouse.
Later, Harthouse meets Tom, and genially tells him that he ought to be more grateful to his sister for all the financial help she's given him (which is considerable). Tom then reveals that the debt he's gotten himself into is yet more considerable, almost weeping with self-pity as he makes this confession. Mr. Harthouse, while restraining the urge to pitch this pathetic whelp into the pond they're walking beside, calmly tells him that he'll help him out a bit, if only he'll act more affectionately toward his sister. Tom agrees. As Tom's behavior improves, Louisa smiles upon Mr. Harthouse, thinking gratefully of him as her brother's benefactor.
It is remarkable how easily this worldly man can manipulate both Tom and Louisa, getting them to think the best of him with his pleasing speeches.. Louisa has led a life so empty of affection that she appreciates the little Tom shows her upon Mr. Harthouse's urging, and so falls prey easily to Mr. Harthouse's manipulation of her unexercised emotions.