Me: “Joseph Smith is telling the truth because Joseph Smiths writings say so.”
Your response: “If you belief he is a prophet of the living God, then yes.”
You are still relying on circular logic. The same could be said, and be as valid of an argument, if one substituted the name Jim Jones, for Joseph Smith.
Belief that a man is a prophet does not make him one, in fact the Bible specifically says there will be many false prophets who many will believe in.
And the bible also says that there will be real prophets, living prophets.
Whom do you all consider to be real prophets?
We all know there are false ones, but who do you think are the real ones?