A recent article reported that a purported self-defense instructor is being investigated for fraud. See the two articles here:
Apparently David Portnoy, the "instructor" in question, has gotten around. Here's an article from Depauw University several years ago:
And David Portnoy made it into Snopes.com, the hoax-busting site. They say that if statements attributed to him are so, then he "should be characterized as a fear merchant vending false information to those anxious to feel safe." See http://www.snopes.com/crime/prevent/rape.asp for their whole article, which is very worth reading.
Apparently his approach is to offer a free self-defense seminar, then use scare tactics and manufactured assault and rape statistics to sell over-priced pepper spray.
And the moral of this story is to yes look a gift horse in the mouth. Or at least through the internet. If those who booked Mr. Portnoy had done their due dilligence, he would not have gotten in.