I'd say you ought to let the homeowner know about your suspicions and recommend that they contact their insurance company and/or a reputable testing company. Tell them to beware of scams.
The 2009 Chinese drywall controversy is a health and safety issue involving defective drywall manufactured in China and imported by the United States starting in 2001. Laboratory tests of samples for volatile chemicals have identified emissions of the sulfurous gases carbon disulfide, carbonyl sulfide, and hydrogen sulfide. These emissions, which have the odor of rotten eggs, worsen as temperature and humidity rise and cause copper surfaces to turn black and powdery, a chemical process indicative of reaction with hydrogen sulfide. Copper pipes, wiring, and air conditioner coils are affected, as well as silver jewelry. Homeowners have reported a variety of symptoms, including respiratory problems such as asthma attacks, chronic coughing and difficulty breathing, as well as chronic headaches and sinus issues.