Usually the numbers from brokers and listings are hopeful, misleading or just plain wrong and you need the ability to find the right numbers and underwrite from those. 

@Assad Oskuei you're going to want to talk to the Cranston building department.My understanding is that ADUs in Rhode Island are limited to the current owner and only for family members, so you wouldn't be able to AirBnB or rent it out, and the ability to have someone live in it wouldn't automatically transfer to a new owner unless the new owner applies for (and qualifies for) having the same in-law unit.ADUs in RI are much more limited than in other states, for example California.

You should be able to determine a pretty accurate market rate within a day or two.I agree with Matthew that you should seriously consider a property manager.

I think I have good idea of how to determine this number in single family houses but struggling with the commercial ARV.

No, where you went to college has absolutely nothing to do with your ability to succeed. 

I must say that there was a time many years ago when I was struggling to rent a place and it was someone's ability to offer me housing that saved me from homelessness.

In this case you'll need to determine your financial activity and pick a solution that will work for this.

My expectation was never to buy here, but to save money working here because the money making ability is higher (like you said, the rich and famous).. and that's exactly what I have done.

Then she’s presented with a bill. 

Of course there are tons of questions a Landlord can ask a manager to determine if they may be a good fit.