The simple answer is "if you can't pin it down" don't trust it.
Claims that can't be proven by the person making them should be taken with a grain of salt---just how much salt you need depends on the claims.
Sure, it always possible that someone is setting up an elaborate con--but its harder to pull off than you might think...over time anyway.
If a persons claims are "jello" then that is a red flag.
By itself, maybe nothing, but added to other red flags--a pattern starts to show up.