Political candidates' speeches are loaded with promises and with expressions of good intention, but one must not forget that the politicians' purpose in giving these speeches is to get themselves elected. Clearly, then, these speeches are selfishly motivated and the promises made in them are unreliable.
The argument overlooks the fact that a promise need not be unreliable just because the person who made it had an ulterior motive for doing so most accurately describes a flaw in the argument above.