Doing pre-employment drug screens. 

Or the property manager has a history of stealing client rents to support her drug habit.How do you vet the people you need helping you when you're hundreds or even thousands of miles away?

The problem is that there are laws on the books that allow the federal government to seize and forfeit any money from the sale of illegal drugs and to seize any property bought with proceeds from drug sales. 

However, certain types of crime, such as burglary, assault, arson, sex offenses and drug dealing convictions will be more relevant than traffic offenses, and older convictions are typically less relevant than newer ones.Avoid the Small and SpentIt is illegal to refuse to rent to someone because of past drug use, though you can consider a history of drug manufacture and dealing.

I suspect drug activity in one of my apartments and would like to know if it is possible to run a drug / chemical test to expose the situation.

First and foremost, if I borrow from a "hard money lender" who has funds originated from a "Drug Cartel" or an "Organization Sponsored by ISIS" or any other shady resource, how would I know?

That way all the drug dealers, illegals, prostitutes and people of all kinds that don't pay Income Taxes, will end up paying.

I have taken up an interest in real estate investing after reading Rich Dad Poor Dad by Robert Kiyosaki earlier this year (from what I read on the forums and heard on the BP podcasts so far, this is a popular starter drug among investors).

Unfortunately, in my market, you can't even get a rundown drug house for 100k.

Off the subject but you may want to go see the film The Infiltrator; shows how the drug business works.