The other option after that would be look up the City municipal codes, specifically for the regulation authorizing a casita on a SFR parcel.

If a broker or a lender originates and funds a loan (either from their own funds or on a warehouse line) that doesn't conform to the current zoning and it doesn't have "legal non-conforming" status with an explanation of the current zoning on the first page of an appraisal form 1004, and subsequently a 100% rebuild letter from the zoning authority, that loan is considered "unsalable". 

We are trying out use of Landlord-Tenant Authority Forms and waiting for results. 

But when searching for an entity, you still have to list yourself as an authorized person / member so in the end is there really any point to get a virtual office address?

I talked to the seller,  (a lawyer) who had the same opinion that I had: The improvements were made before we had walked through the property and they weren't authorized by the landlord.

I am reading a book that may be of interest to you: the author develops high end mansions in southern Florida. 

Would your underwriter authorize a policy w/o an exception for the restriction?

Since the taxing authority doesn't care or know any better, they will sell homes without HUD seals so be careful.Beyond that, you will definitely find newer and better used options at repo lists (21st Mortgage, Vanderbilt, etc.) on Craigslist or Facebook, and from home wholesalers.

The second is you had the apparent authority to bind the corporate buyer. 

The title company will verify authority to sell.