The presence of unpleasant odors in the house can mean many things, the most common of which is smell. Biological problems like mold can be difficult to treat because there is usually a lot of work that needs to be done to fix them. Changing the walls is the most common "fix" for mold, because it can try to find the source. Visible residue can be killed with bleach, but the problem usually runs deeper than the surface. Professional inspectors must identify any defects that arise after due diligence and communicate them to the real estate or home buyer.