@Josh Yame the rent for the garage 1/1 ADU will often be a bit lower than a comparably-sized 1/1 apartment--but that's partly because apartments often offer additional amenities (like a pool, a gym, etc.)....and the house will be lower rent than a comparably sized house without an ADU (because tenants renting a house would rather have the property to themselves rather than have to share the property with someone living in the garage ADU)....in a lot of ways, a house with a garage ADU is similar to a duplex--in terms of functionality, rents, tenant pool, etc.  ...So, if the garage is 1/1 and the house is 3/2, I'd try to comp the rents to a duplexes with one 1/1 unit and one 3/2 unit--that will get you in the ballpark.Regardless of the type of property, I like to be very conservative with my numbers; I'll often assume 15-20% lower rent than the market, and I factor in lots of vacancy.

Once you have a short list, get an account with each one and run them through the wringer to see how they really function.

Our reason for NOT pulling one, is there are functioning businesses in the building, and the seller does not want to risk an issue that would cause loss of rent or un-realistic requests from the municipality that may disrupt the commercial tenants. 

It tracks and collects your tenants payments, and automatically deposits into your bank account and SO MUCH MORE… applies late fees, tracks tenant / unit expenses, has a tenant facing web portal for reporting maintenance issues and collecting rent and on and on… screens new tenants, broadcasts your rentals for rent, etc!

I'd take the fully functioning app that saves me hours every week for only $50 a month.

It was a lot of work but the value of my property has grown exponentially from it (I just refinanced and pulled $150k in equity from the property) AND I never get maintenance requests for that property because everything is new and functioning correctly.  

I'm under contract for an 8plex that has a non-functioning common laundry area.

The deck is functional as is, I bet, and the sellers know that. 

The floor plan and exterior land usage was functionally obsolete but had the potential to rework it and significantly improve the property.

The floor plan and exterior land usage was functionally obsolete.