Me, too. Not throwing this at AZgrandma, but if you (general you) know that a person has a propensity to lie sometimes, then it would be natural to have the tendency to not believe anything they said. You would find yourself doubting them when they were actually telling the truth. In short, you just can't trust them. You end up doubting them no matter what they say. If they tell you the sun is shining, you look out the window to see if it's raining. It's just human nature.
I have a brother who likes to exaggerate things, and flat out lies occasionally. He does not lie to hurt anyone, he just likes to tell a good story and make it a better one by embellishing a little. I've tried to imagine if he was placed in this kind of situation, and the more I thought about it, I realize that he would probably not veer from the truth if it's something this serious. He would tell the truth no matter what. I'm not saying this is what Mark is doing, just that liars don't lie with everything they say, sometimes they tell the truth, it's just hard to distinguish the difference.
No reflection on AZg at all, just saying that even a broken clock is right twice a day.