[Hmm... That's a tough one...]

I suppose it depends on the circumstances... Each of them are so very different, aren't they? Personally, I'd try to gain their faith by being myself; faith isn't a simple subject, but as long as you're putting your own trust in someone, over time, they'll often become more capable of returning that faith.

I can't say it's always certain, but I can't think of many things in life that are.