Quote from @Marcela Hoag: Start with a cost:benefit analysis.

There are so many problems with your analysis.

What is the market value of a bed room and a bathroom  for the purpose of Comparative market analysis. 

You could probably do a NPV analysis on that compared to the price of installing a water softener up front.

It's impossible to give a definitive answer on whether you should sell or keep the property without the address and further details but based on the photos alone what I would first suggest is an amenity analysis.

I feel as if it's better to deny them at this stage before they even pay for an application.

We sent over our cost analysis and the reasoning for our offer and because the numbers made sense, the seller agreed, and we got a great deal overall.

After a few minutes of analysis, I knew I had to find a way to make this deal work quickly.

Even at 18 you may have some skills that you have learned like sales, marketing, research, data analysis, and others. 

You can virtually empty and stage rooms, and even do landscaping, all within a photo!