I was sent a personal message by somebody saying that the burden of proof that something is a scam should be on the person accusing the scammer. If they can't PROVE it, then they should shut up.
I disagree. I think the burden of proof is on people "guaranteeing" high returns.
Here's how I think of it:
Imagine you see somebody claiming they have invented a perpetual motion machine.
You claim bullshit, because that's against the laws of physics and all previous experience.
Now they send you an email, saying "... before making such accusations you need to PROVE that it cannot work."
Foolproof schemes to make high interest at low risk are the financial world's perpetual motion machines. They do not exist.
Perpetual motion machines may not be scams; there are misguided people who really do believe that they've violated the laws of physics and will prove all of those pesky scientists wrong. I'm sure there are people who truly believe that they've invented foolproof methods of investing lots of money with no risk, too, but I'm equally sure they're delusional.