Actully, being a magician in most cases (unlike me, I do a lot of free work) is like anything else - know your worth and charge it.
Easier said than done unless we adopt the economy model I posted about. But, if you can get clients to pay your worth, do so.
However, as the magician, you would be ethically responsible by matter of fact in the art, and to be honest in workings. But know your worth.
As the client, you are responsible for keeping an open mind, and expecting the positive outcome. You have the right to not be gyped.