Some of them are undoubtedly "in it for the money," but most are probably very sincere in their belief that only people who believe as they do will go to heaven; all others will go to hell forever.

Since they believe this so sincerely, some of the missionaries will resort to various tricks and devices to persuade you to believe like they do (the "Moonies" call this "heavenly deception"). We make a mistake when we assume that sincerity - in and of itself - is necessarily a good thing. Hitler was most likely also quite sincere in his belief that the world would someday thank him.