In this image is a duct for a clothes dryer. As you can see it is in desperate need of being cleaned.
Having too much lint build up is not only slows the flow of air, increases the drying time and increases the costs of drying your clothers. A build up of lint such as this is also a fire hazard. This is just one of the things I come across while doing home inspections.
If you wish use this information as a reason to keep in touch with your clients (past and current),