A liar is someone who knows that what he’s saying is not true, and he wants to deceive you for his own personal gain and/or to protect himself. He doesn’t necessarily want his lie to be true. He just wants you to believe it so that he can get on with his plans.
A bullshitter, however, while not speaking the perfect truth, wants what he’s saying to be true, and he wants you to want it to be true as well. He will over exaggerate his statistics to make things appear to be better, or more worthy of praise, than they really are. He knows it’s bullshit, he feels it inside, but he convinces himself it’s true just long enough to blurt it out. He hopes that you won’t look too deeply into what he’s saying, and he knows most people won’t.