His epistemological tools do not lead him even close to the truth, so you can assume he is wrong about everything.
Like I said before, the scientific method is the best tool we have, anything else can easily lead you to mental masturbation or worse, delusion or schizophrenic episodes. You know the I am the prophet, I have found the light type of conditions.
Translation: His arguments lead to conclusions that falsify what I have arbitrarily and subjectively defined as "truth" so I am going to assume he is wrong about everything and stop thinking about his arguments.
I'm not assuming anything, you are. Your arguments show humans cannot determine whether something is true or not. It's also really easy to prove that using the scientific method works far better than simply using your reasoning and logic. For example:
Let's say you don't know much about anything. An apple falls on your head, you start to think about it, why does that happen? Will you ever be able to determine it's gravity only using your logic without performing any experiment or gathering evidence? Of course not. In fact logically, the earth could simply be accelerating upwards, that would make sense logically and would explain the apple falling.