Jim, I see rusty nails every day in basements, crawl spaces, attics with no accompanying mold-like substances. Is there humidity and water vapor condensating? You betcha. Just because nearby metal has some surface rust, it is a bit of a leap to call out "mold". Even though you may be right, be prepared to answer questions if it isn't.

I refrain from trying to label hazardous materials such as asbestos, mold, lead paint etc. in my reports. I will look for these things and I am damn good at finding them, but I don't have a mobile lab at hand to accurately identify them without a doubt.

So, I provide a detailed photo, and point out that due to the genre, location, appearance, it may be one of these above named substances.
And I provide links to the EPA website which applies. They can take it from there.

Now if you happen to be one of the many inspectors who are licensed, schooled, and insured enough to make these calls with complete confidence, have at it.

I am of the ilk that it is best to do one thing very well, and not a lot of things not as well. We gave up septic inspections for that reason.

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Keep L@@kin