Do Take My Class for Me sites really work?

Has anyone used one of those "take my class for me" websites? I keep seeing advertising promising to handle your online classes, assignments, and even exams, but it all sounds too wonderful to be true. Do they truly deliver on their promises, or is this just a scam waiting to happen? I'm curious if anyone has had any real-world experience with a take my class for me service and whether it was worth the money or just added to their stress.