It only grows when it has access to moisture and a food source (dust, food, etc.) and will go away if you remove either of those.

We went with his plan, but this inspector won't allow outlets from both apartments in that side as he considers it penetration of the fire wall.We are exploring the fireproofing that spray foam offers thinking we can fill the cavity and eliminate the cavity on one side.

If you can answer any of these questions, I'd truly appreciate it:-As California's AirBnB market gets more regulated, is it worth trying to penetrate into this market?

On a slightly more serious note a large capacity fan that vents outside tied into the light switch so when the light is on the fan is on is a good way to move moisture out of the room. 

Doing some research it looks like I can do a moisture barrier and sub-floor - not sure if that'll help improve things.

This would allow water to penetrate the building and potentially damage the structure.2.

I learned that on the next deals to look for moisture in flooring and walls to better negotiate pricing.

It was noted that there was moisture stains on the eaves & soffits and to have a licensed contractor inspect.

I can clearly see moisture on the wood under it, but no signs of a leak upon my inspection as well.

The moisture/mold issues are particularly concerning to me.