I conduct "visual inspections" as such, I word my document as follows:

"a mold like substance was observed at.... location"

I do however, depending on the severity of the problem, have private words with my client.

mostly it would go like this:

"most surface mold/mildew can be taken care of with bleach."

or...
"unfortunately, I can't tear that wall out to look behind it. But, what you see there is usually indicatve of a moisture problem that needs correcting."

or......
"the only one who will be able to tell you exactly what it is, is a Micro Biologist"