This quick turnaround showcased the power of market timing and effective negotiation, doubling the initial investment in just one day.

Even a contractor with 30+ years of experience only knows what they know - so, they may not know the most cost-effective solution:(5) Political trends that may lead to more controls on landlords - being forced to accept S8, not being able to deny for evictions, rent control, etc.

What is the most cost effective route to take?

Google ads (not free but can be effective when done properly)4.

Taking 'effective' action is what you need to do next, find out what your goal really is and work backwards in discovering what you need to do to achieve it.

No previous tenants or current tenants complain of the mold issue or have any side effects of the mold.

Wondering if they are as effective as the website indicates? 

I'm in Chicagoland and we have what I call a "seasonality effect." 

Start by targeting your audience more effectively—hone in on vacationers, outdoor enthusiasts, and families that would love your location.Also, consider looking into property management services that specialize in short-term rentals, or even investing in some marketing tools to help boost visibility.

That means effectively pricing your rental to others in your area and even looking at apartment rent rates to compare with your SFH.