Drug trafficking, sex trafficking, prostitution, people hiding from the law, etc.  

@Kunal Lakhwani I do not want to say anything about the wrong company, but I would double check that the owner of one of those companies was not recently arrested for underage sex trafficking.

There are 3% rent increases built into the leases and I can bill the tenants for increased CAM expenses, taxes and insurance.Am I missing something here?

"In the state of New York, anti-discrimination laws cover most types of housing, with four main exceptions:one- or two-family owner-occupied buildings. room rentals in housing for individuals of the same sex, such as college dormitories or boarding houses where all residents are of the same sex."

Which may not be all the problems - they don't always get everything.A sewer cam might also be worth thinking about.

I don't know MA laws, so generically:1) Do you need any lead paint, bed bug, or sex offender disclosure? 

It would be wise to order a home inspection from someone who does duplexes.It would also be wise To order a sewer cam inspection.

However, sex workers don’t always come with drug activities.

They are saying it'll report "crimes at a national level like national sex offender list" but that they can't access county or state level offenses.

All tenants paying CAM charges.