I aim for honesty, even if it's negative.
If it's someone I like and I don't want to be honest with them because it would hurt their feelings I'll lie as convincingly as possible. I do this sparingly so that it's believed.
If it's someone I want to feel bad I'll change the subject or answer...
As far as veracity is concerned the only difference between Scientology and any other religion is age.
If you believe that a man was resurrected from the dead after 3 days, that a snake could talk, that Muhammad split the moon in half, that a horse could fly or that thousands of years ago...
Even then there are a lot of people who would know, eg.
Chris Chibnall
The actor himself
The actor's agent
Higher ups at the BBC
Whoever does the CGI for the regeneration
The companion (unless he regenerates alone)
And likely the families of all of the above. You'd also be able to narrow it...
Not really possible, hundreds of people would know who it is before then because they'd have to interact with him during filming. There's no way the media don't find out.
Moffat couldn't be arsed with it most of the time either, spent a great deal of time on Sherlock which is why the seasons were so disjointed in his run.