I tried to explain that their business model wouldn't work very well if they told their customers that the place is ghost free - tough to sell the follow up full cleanse on non-haunted places.

But first you must know your business model.

Your biggest challenge is not class, it's size.  18 units is too small for onsite management and a different business model than SFR management companies have (no apartment vendors, slow unit turns, retail pricing on maintenance). 

It's a model that allows an investor to keep growing their real estate portfolio without having to continue spending on high quality protection.

Commercial properties typically need a refresh every 10+ years anyway.If rates are rising, it's typically due to a strong economy, which is typically accompanied by rising rents.And the captain obvious comment...modeled results should be stressed tested for changes in rents, occupancy, and interest rates.

That way if he doesn't work, he doesn't get paid.If it works out well it could expand your successful business model to another market.

In using this approach of looking at the worst case scenario, consider running a model where you have 50%-60% occupancy in your existing units, interest rates go up 2%-3% over the first 5 years of the loan, and (if there's rehab) that the costs are 25% above what you estimate.

Most importantly though, if someone doesn't want to live in an area, it will be a very hard business model to maintain, and challenging to find good quality tenants.

Their business model may strongly depend on nobody looking too closely. 

Goals, business model/knowledge, financial situation, and preference.