Innocent until proven guilty, sure. But with this one it is unflagged until victim proves scammer guilty. If no victim acts on the flag, then nothing is done. You are not allowed to flag without first being scammed.
No, you are just not allowed to use the
high-power scam flags -- intended mainly for punishing people, not really for preemptively warning about scams -- without first being scammed. You can still use the newbie-warning flags and negative ratings, which have plenty of warning power.