I taught an heirloom sewing class -- made up kits with expensive fabrics and laces to use in the class. 3 or 4 people who had signed up didn't show up for class. I didn't make enough from teaching to cover my expenses. Never again! I do think that special circumstances could be dealt with but having a waiting list doesn't always work -- the person next on the list doesn't have any advance notice in order to get ready to take a class.