I had a thought…
Most people who practice magic tend to excel in one area or another, i.e. love, money, protection, healing, evocation, divination. While a good magician can perform any of these acts, they will usually have something they specialize in.
My idea is to have an exchange of different types of services between magicians to help each other. An example would be one person performs a love working for another person and in return they would do a money working.
I think this would work best if no money was involved, just trade one favor for another.