Taking air samples for mold spores is easy. Knowing how to interpret the laboratory results is another matter.
There is no one level of mold that can distinguish a clean and moldy building. Outdoor spore types and concentrations have an important influence on the indoors. Unfortunately, the outdoor types and concentrations of mold vary quite widely over time and space. In other words, some climates during certain times of year will have extremely high concentrations, and other climates at other times of year will have extremely low levels. We can compare the indoors to outdoors, but realize that the outdoor concentration is a moving target!