This is a tough one. But lets try. One good way is to establish what was the thaught process of a person making a prediction that lead him/her to say all those things.
If the thaught process is not consistent with logic, established nature laws (within bounds of their applicability) and plain common sense than you should just disregard what they say and flag them as attention seeking individuals.
Serious and intelligent people have a solid reasoning that doesn't sound like a science fiction writters brainstorming session.
So in short: check facts, chech thaught process. If anything misses here than it's bs.
Hope that helps.