If your home has a mold problem, or any other defect, do not hide this fact! It is unconscionable what this seller tried to hide. See the story of the Secret Room that I found over at the Sellsius blog
REALTORS are obligated to provide notice of defects that they are aware of through a visual inspection of the property, even in seller did not disclose the defect. And, even if a mold inspection was requested in the offer it is not a guarantee that a Home Inspector would have even discovered such deception of the "secret room". Full disclosure is the best practice. For buyers, inspections are yours for the asking. But these must be requested in writing in the offer to purchase.