At that level, "percentage" is an insufficient measure. You want "permillionage", or maybe more colloquially "DPM" for "Defects Per Million" or even "DPB".
You'll still get false positives though, so you provide an appeal process. But what's to prevent the bad actors from abusing the appeal process while leaving your more clueless legitimate users lost in the dust?
(As the joke goes: "There is considerable overlap between the intelligence of the smartest bears and the dumbest tourists" [1])
Can you build any vetting process, and associated appeal process, that successfully keeps all the bad actors out, and doesn't exclude your good users? What about those on the edge? Or those that switch? Or those who are busy, or wary?
There's a lot of money riding on that.
[1] https://www.schneier.com/blog/archives/2006/08/security_is_a...
Yes, it's pretty simple. Create and enforce some consumer protection laws which require, for example, that any company larger than a certain size is required to establish support offices staffed by humans in every major town. And required to resolve every issue within X days either by fixing the problem or clearly documenting why not. If not, no arbitration allowed, so they are subject to lawsuits if the reason doesn't hold scrutiny.
Problem solved. Companies like goog, facebook et.al. can easily afford this and it'll stop this ridiculous behavior.
It also to some extent protects the companies. Spambots who create a million accounts can't replicate a million humans to show up at the support office, so it establishes a human:human relationship that's completely missing today.