A large number of false positives would likely show up as a deluge of negative reviews. "They charged me $500 and I've never smoked in my life". Surely some of

A large number of false positives would likely show up as a deluge of negative reviews. "They charged me $500 and I've never smoked in my life". Surely some of those would be lies, and you'd have to dig them out from the existing pile of petty grievances that result in bad reviews. But I suspect it would still be pretty clear if there were that many false positives.