I can't tell, I feel like I am among the minority even at this forum that does believe he was the real McCoy.
I assert that aside from the obvious, (time travel not invented yet) I feel there is more evidence that suggests truth than the contrary.
My biggest reason is that after 25 years, he has never tried to financially gain from the fame. What John did wasn't illegal, because a hoax with no harm = no foul. If I claimed I was from Mars, it doesn't break the law. If I said I was from Mars, and you can visit by jumping off the Empire State building, then there could be issues.
He has had many opportunities to exploit the Titor copyright. Producers from Disney tried to take control of the Titor name but were blocked.
Someone is protecting that copyright. Why protect it, if it were a hoax, wouldn't you just cash in?
That is an example of peripheral logic in favor of it being true.
I think the extent of time of being on a forum full of doubters would prove too much for anyone to stay consistent the way he did. I have watched interrogation documentaries and compared to this forum, an interrogation would be child's play. I've seen innocent people under a fraction of the pressure fold to unable to keep details straight.
John underwent this forum's scrutiny for almost two years, I think, and he was pretty consistent, despite people claiming major inconsistencies.
Anyway, I could go on and on.
*Personal Context* I have heard a lot of traveler stories, because I find it very interesting. This is the only time traveler story I believe.