In fact I would go so far as to state if a contractor says they shall be using bio-cides or antimicrobials to eliminate mold at home I would look elsewhere. Toxic black mold require a period to develop and so they often manifest in moist and damp areas like corners of ceiling, walls, drywall, kitchen corners, bathrooms etc. Some furniture, such as mattresses and sofas, may hold water within that can enable the mold to return.