For those vacant those are even worse as I have had a few end up in the red.

Another huge red flag.Hope this helps.

Does the historical society in a certain town have a huge issue with ripping down old falling down red barns and fight people in court over it (Leaving the owner with an eyesore and a dangerous item on their property that costs them insurance carriers every year)? 

@Annie Li  This is a BIG red flag.Your contract should state that the property is to be delivered vacant and broom-clean. 

😱A ton of red flags here! 

How are you validating your renters because he’s a huge red flag! 

A great agent will bring up and address things you haven't thought of, good and bad.They will have ideas for physical spaces, ways to increase income or reduce expenses and bring up pitfalls or red flags to address and account for.I am still seeking said agent.

Somerville is red hot, I think the only play I would make right now in the ville at this point would be to try to find a value add multi that I could add another unit (RB zone with enough land sq ft).

What are the big red flags I should be looking for? 

It's more helpful I think to go once you know who some of the players and the names are so you know who you're meeting.