One thing you should consider is checking the sex offender registry in those markets, you might be very surprised at what you find.The NEREIA in Chelmsford usually has a PM or two but not anyone I can recommend.  

So when they say they have 3 big Pits, or are a sex offender, or just got out of jail, etc. 

There are many co-ops in NYC and I've heard plenty of stories about a co-op board rejecting a buyer because they thought they wouldn't be a "good fit" for the building.. these were celebrities usually who the board thought would be partying to much probably but basically any excuse will do other then race, sex etc...

Just gender, race, sex, etc.

These laws prohibit discrimination based on race, color, national origin, religion, sex, familial status, disability, and other protected characteristics.2.

-Can property values decline due to registered sex offender living in area?

You run the criminal background check to confirm if a applicant is a sex offender.Bottom line is you still have the ability to reject any applicant you choose for personal reasons even if it is their appearance, attitude smell etc.

My second thought was how much I would hate to be across from a school if I were renting it - the noise level and the periods of high traffic in the area would be downsides I'd be sure to mention in a review.My advice would be: if you want to move forward with it, look into the local laws re: convicted sex offenders to make sure you can conform to them, and prominently disclose in your listing that you're across from a school.  

I've heard about signs like these and they are possibly sex trafficking rings.

Which includes: criminal, credit, prior eviction (wouldn't help now with Covid,) plus checking their sex offender status and social media.You would think that those screenings are enough, I know I did.