I'm considering building a second window,  that would serve as a security measure, utilizing the space i have now,  and using a metal,  chicken wire type screen over sandblasted glass. havent had much luck on craigslist or ebay. 

Have a iron clad lease agreement.

I own a class c complex with 6 units of 2000 sq feet each that is 2 offices, bath, and shop for 12000 sq feet, and a pole barn type storage building that is tin metal, about 8000 sq feet total with 3 tenants. 

Two buildings totaling 10,000 sqft, but 2 acres is paved and has metal awnings around three sides with 18' clear.

Metal R panel roofs are in the 550-650 range.

The "mold" looks like it is more likely dirt and dust coming out of the register when the air is on, and due to the humidity in FL sometimes you'll get condensation on the metal register(metal gets and stays colder than everything else and small amnts of condensation form) and then the dust sticks to it.

When doing a virtual drive by, some things you may want to be on the lookout for are chain link / metal fences around every home, trash / broken furniture out in the streets, stray dogs running around, uncut overgrown grass, broken down cars in people's drive-ways and lawns, bars on the windows of the homes, etc.

You screw in two metal brackets and click it in.

A Heavy Metal Rock band that practices their music at all hours of the night.

Most likely it;s the listing agent who is not outting the pedal to the metal....... get to them and force your position.....good luck