There's no question that IAQ can be quite subjective; certain people will always be more sensitive to odors and airborne contaminants than others. Indeed, there will even be individuals who complain about their indoor environments without any known toxins present in the air. That can make it difficult for engineers who are brought in to determine if an IAQ problem truly does exist.
Some of the elementary schools in Baltimore County (MD) were faced with such an issue in the mid-1990s: Students and faculty were becoming sick in one particular school, and in reality, severe problems were found. Then occupants in other schools in the district began complaining that their indoor environments were also poor and needed help yet, "smoking guns" were less obvious.