so he has an initial negative equity in excess of $100k.so -$100k / (a very small cash flow when properly allocating for expenses and vacancy) equals years before there is any cash flow.  

Quote from @Alvin Sylvain: This could be a good idea if executed properly.

From software issues that the manufacturers refuse to help you understand, to hardware issues like the joysticks easily pop into the machine when kids bang on em.

Overall, for every type of property....I would say that keeping up with proper maintenance is what most people neglect.

The typical clients that seek out cost segregation studies include:Real estate companies that buy and sell multiple properties each year.Individuals with a portfolio containing investment properties including apartment buildings, multi-family homes and even single residences.Franchise owners with properties that are similar to one another such as assisted living facilities, storage facilities and golf courses.Business owners of hotels, food facilities, shopping centers, restaurants or manufacturing plants.It depends on the type of property, but generally 15-45% of the building’s costs can be classified into assets with a shorter life.

You must give proper notice before each showing, you must give the renters the opportunity to buy the house first, and the new owner will have to honor their lease if they intend to stay.

Do they have the proper insurance and licenses?

Just know them going in so that you can properly budget.

Just need to stat under the occupancy limit.Also keep in mind basement needs to be livable square footage, ie have egress and proper ceiling height. 

Give proper legal notice of non-renewal and get them both out.