There was actually a time not too long ago where police would investigate crimes and DAs would prosecute the criminals.

I know most of us have heard horror stories and/or have personal experience about criminals and unsavory characters taking over vacant properties then claiming squatters rights to avert the authorities. 

Good idea except I'm not able to get a realtor's license because I have a criminal record from way back when.

Especially now that you've posted your suspicions on a public forum, I'm not an attorney, but I've watched enough Law and Order that I could see there being the possibility of you being charged for "Aiding and Abetting" their crime by not reporting it or "Criminal Facilitation". 

Here's a excerpt from one group of scammers brought to justice.

In FL I had a guy who confirmed my criteria and then was upset when I denied for a criminal issue in the background check...because he plead 'no contest'.

Otherwise, the criminal case can serve as evidence in suing them in small claims court. 

Anyway my question to you all, especially the criminal masterminds here on BP, is how can I really mess with these scammers?

How many tenants sue you for discrimination, probably not that many, but plenty of free legal clinics around who would just love to help tenants get justice and teach you a lesson. 

It will be nation wide as soon as the Department of Justice approves the settlement.Don't like it?