IIRC you can make it significantly more difficult with certain approaches, e.g. there's an OAI approach that uses zero-knowledge proofs and that seemed pretty sound upon first inspection, but as far as I know the current best answer is no. But you might want to try to answer the question yourself, IMO it's fun to think about from a cryptographic perspective.

Probably (in practice; in theory it looks like a natural aspect of decision-making); this is too poorly understood to say what specifically is necessary. I expect that if we could safely run experiments, it'd be relatively easy to find a well-behaving setup (in the sense of not generating predictions that are self-fulfilling to any significant extent; generating good/useful predictions is another matter), but that strategy isn't helpful when a failed experiment destroys the world.