The most useless waste of time and energy in the martial arts community - but admittedly very common and sort of fun to participate in - is the debate of style vs. style.
Just pure style versus style: Kung Fu vs. Tae Kwon Do, Brazilian Jiu Jutsu vs. Shotokan Karate, Ninjutsu vs. Kalaripayattu (I would pay to see that fight)... we love to get into these debates, and sometimes, we confuse art vs. art arguments as being fraud busting.
So let's talk about the difference.
As I've written before, the only difference between various styles boils down to differences in strategy for dealing with (and committing) violence.
That's it. That's all there is.
Turns out, there's a whole lot of different - and valid - ways of dealing with violence, and there's more than one context in which violence might happen. Just because a style's strategy doesn't fit your own world view or talents or the way you assume violence will occur, doesn't mean it can't or doesn't work for someone else.
So, Mr. BJJ guy, just because you don't like, say, Shinto Ryu's approach to training and dealing with violence, it doesn't automatically make what they do or teach fraudulent.
It's a difference of opinion.
So let's get into fraud.
Fraud is engaging in dishonesty or deceit or cheating in order to gain an unfair advantage or profit. In the martial arts, this comes in two main flavors: representing a technique or action as being effective when it's been absolutely proven to not be, or, lying about training or credentials.
The second one is pervasive, unfortunately. There's plenty of belt mills and fudging of resumes, partly to make money, and partly to boost individuals' egos and wish fulfillment.
Most of the time, these sorts of fraudsters can easily be detected on the mat. If they're lying about their training and skill, other skilled martial artists can often tell. This is why they might bluster about "coming to see them" but when someone accepts, will find every excuse or trick in the book to avoid getting on the mat and proving their claims.
However, sometimes, these people are actually good natural fighters, they're just lying about their background. It's still incredibly unethical, and me, I wouldn't train with someone lying to me about what they've trained and who they've trained with. That's completely untrustworthy behavior, and given what we do, we should never allow or reward liars or give our trust to people shown to be untrustworthy.
In my opinion, allowing or ignoring people lying about their training backgrounds leads to allowing or ignoring other worse (and abusive) behaviors.
Yes, this needs to be called out, at least so that people know what's what and can make an informed decision about training with people who lie about their background.
Now let's deal with the type of fraud where someone deliberately represents something absolutely proven not to work as being effective.
This is less cut-and-dried than it sounds like it should be, and here's why:
Human beings come in infinite variety. Some people absolutely react to pain in a very obvious way, and some don't. Some people are easy to knock out, some aren't. Some people are very strong, and some aren't. Some people are very flexible, and some aren't.
Add in factors like illness (mental and physical), drugs or alcohol, weird variances in anatomy (that absolutely happens, y'all, we're not all stamped out identically from a factory, y'know), adrenaline, psychology...
Very little of what we do can actually be proven to be 100% effective on all people in all cases.
It is impossible to test what we do against everyone in every situation that might arise. We work the odds - the odds of such-and-such working is high so we choose that thing instead of another with lower odds of success.
We learn the odds of what works through experience and testing. Ideally pressure-testing with resistance and a culture of skepticism (that's not always completely possible, though, so remember that). We should also cross-train against people who are not buying into our world-view so we can check our assumptions about how violence happens and who perpetrates it.
If you do all that, you'll find that very little is out-and-out fraud (deliberate misrepresentation is fraud, being wrong is not) and very little is 100% completely ineffective in all situations and against all people.
Some things just have very low, but not zero, odds. You or I might not choose that thing, but it doesn't make it a lie.
So, be very, very careful before you start claiming that such-and-such style is a fraud because you don't like their strategy or agree with their worldview. Also be careful before you claim a technique is absolutely fraud, because sometimes we'll be able to find an example of it working in real life (real life makes liars of us all, y'all).
But people who lie about their training background?
Screw those guys.