Your Mold Test is Normal. You Still Suspect Mold
An air sample only tells you what was captured in that sample. It doesn't tell you where mold is.
I start with the building.
Which walls are suspect? Then testing can be directed toward the places most likely to answer the question.
Case Study: The Nose That Knows
A freshly painted home for sale looked excellent and had already produced good mold air-test results. My client wanted a second opinion. Rather than repeating the room-air testing, I investigated the walls themselves. An electrical outlet—effectively an opening into a wall cavity—provided an odor clue. I isolated several suspect walls, tested the cavities and found the hidden mold the previous room-air testing had missed.
The sale ultimately proceeded after the problem was identified and addressed.
This exact predicament appears in current search results: negative mold test but persistent mold/musty odor.