Faith is all they have, as far as I know they make no attempt to 'prove' they're right, they just 'feel' it or whatever.
Maybe, but some people just hear about god and want to believe. Often as part of a reaction to traumatic events.
Not necessarily. We in the west do live in a culture derived from the bible but we have many different sects. In fact with a lot of people who read they bible they all interpret it differently. Some people decide against joining one of the sects and go it alone with their own interpretations, so they still consider themselves christian whilst also admitting they can't prove it, it's just a feeling or a desire. Some even believe significant portions of the bible but still have the capacity to admit they can't prove any of it.
Usually these theists are more bearable to be around as they couldn't care less if you agree with them or not.