Avoid a diagnosis from appearance alone
EPA notes that a substance that looks like mold may need expert assessment to identify it. Ask the assessor to show the affected area and explain the basis for their conclusion.
Ask about moisture and duct material
Discuss the source of moisture and the condition of the duct material. EPA says insulation that becomes wet or moldy cannot be effectively cleaned and should be removed and replaced. Ask the assessor to identify the duct material, affected insulation and extent of the problem before recommending work.
Do not assume a spray solves it
Ask about the purpose, limits and risks of any chemical treatment. EPA advises understanding the pros and cons before allowing biocides or sealants. This site does not diagnose mold, offer remediation or promise a health result.