Here are two essays on the ethics of close-up magic published in Visions magazine. They are based on my experience as a restaurant magician and the many accounts (mostly negative) of laypersons who have been approached by eager magicians.
The first article, which is very short, is on 'consent' (or permission to perform!): http://www.online-visions.com/other/0512ethics.html
The second is on trust between spectator and magician:
Any feedback would be greatly appreciated!