Artists are service reps anytime they are creating work for money. These are mainly projects/commissions that they take on that is separate from their “passion” art since they are having to bring their client’s vision to life.
If the artist is an independent artist with a big audience then they can create freely and their audience will purchase from them. Even then the artist is at at the service of his audience.
A good artist has to be a good service rep, whether they are creating for one client or an audience.