Paper trail, to be referenced later, so TFG can't be all "huh, never said that, never agreed to that" etc. etc.
https://www.asahi.com/sp/ajw/articles/15953967
Well, having the paper agreement certainly helped last time. (A month ago.)
There's also a Language barrier. So making sure there is a written agreement ensures that both sides understand what was agreed upon.
2. He lies when his lips move. When you're dealing with a pathological liar, there's no reason to believe anything he says that paints him in a good light - until it's been independently confirmed.