There are some types of evil that are not easily recognizable as such. Much like the mountain-top ascetic or the cloistered saint, there is no obvious sign of the darkness that lurks inside Vodai.
A family of semi-retired doomsday cultists, just trying to live a quiet life while tending an apple orchard in the country. Except with complications.
Animals have parasites and diseases, so do plants, there are even bacteria that cann dissolve oil spills or plastic or what have you - why couldn't there be a disease living off magic - a magic item could be infected, losing power and speading the plague to other equipment it contacts, while a magic user would slowly lose his powers and contaminate all he works with or casts a spell at...