The character for which Molière's play, Tartuffe is named, is a sly and very slick conman. And Orgon, the foolish and easily swayed man who Tartuffe dupes, makes the con that much easier. The element that best serves Tartuffe and makes him seem "sincere and well-intended" is his false piety.
Tartuffe presents himself as a devout and holy man. Orgon is taken in by this contrived behavior and thinks his new house guest is a saint. Orgon gets so carried away that he promises his daughter Mariane in marriage to Tartuffe even though he has given her permission to marry another man (Valère); he disinherits his son Damis to make Tartuffe his heir; and, ignores the warnings that friends and family give him. Orgon does not even believe his wife when she tells him that Tartuffe has tried to seduce her. It is only when she makes him remain hidden in the same room to witness Tartuffe's advances that he finally is convinced. By this time, Orgon has be so deceived that Tartuffe has information that can ruin his "patron."
Perhaps Orgon simply sees what he wants to see in the character of Tartuffe, but his foolishness is almost beyond comprehension when Tartuffe is placed above Orgon's own family members. Once he has invested all, as any conman would wish, he is fortunate in the end that he does not lose everything to this "seasoned criminal."