Question

In the field I work in, swindlers are too numerous to count.
What should be done?
There is a WhatsApp group of people working in the field, and every so often someone who got stung posts that so-and-so swindled him, so that anyone who wants to be careful and protect his money knows whom to watch out for.
However, this is not free of problems.
A. Many people do not post.
B. It is hard to follow up on every case to determine whether this really was a scam, or whether party 1 sees it that way, but if we were to get to the bottom of the dispute we would understand that there is also another side to the coin. Of course, it is hard to do that every time..
 
My questions:
A. Am I allowed to save the name of the current swindler in my contacts under the label “Caution: swindler”?
(These days there are apps that show anyone interested how so-and-so is labeled in other people’s contacts, and then his close friends, family, and also anyone who wants to do business with him can see that such-and-such number of people call him a swindler. Of course, he has no ability to investigate every case.)
 
B. Am I allowed, or perhaps even obligated, to pass it on to additional WhatsApp groups in the field so they can beware of the current swindler?
And again, he has no ability to investigate every case…
 
What should be done?