Water that cannot drain sits, sitting water creates moisture, and moisture creates "organic growth".

A vent hood or fan can prevent cooking smells from lingering in the unit and prevent the buildup of moisture and humidity that could lead to mold growth.

various windows would not open wood rot on the deck the extensive growth all over the house (as lindsey mentioned when we saw the property, it looks like the lawn maintenance has not been done in awhile) Basement possible mold evidence of moisture (not a huge concern, but still noted) wood rot amateur repair on the main water supply line (fairly concerning because we'd have to pay a plumber to take a look) Apt 1 Light switch did not work when we visited hot and cold plumbing lines reversed water marks in bathroom ceiling. potential leak.

There's also some moisture on other spot from seeping water in basement. 

The tree’s needles have a wax-like coating that prevents the loss of moisture during winter months.

If there is anything to do with moisture (roof or plumbing leaks) those should also be taken care of quickly.  

With mold, it needs moisture.

Whenever a roof surface abuts a vertical wall, moisture intrusion that may lead to damage and rot becomes a risk at the intersection.

The duplex needs a new roof, new windows, update with the electrical outlet, it has termites and moisture damage (possibly molds) among some other things.

Tenants love the 'hypo-allergenic' flooring--usually solid vinyl planking, although a good quality laminate, properly installed with underlayment/moisture barrier works nicely.