Every Artist on CO:CREATE sets their own policies.
Artists are all running their own businesses, and may handle things differently at their own discretion.
Policies can cover a wide variety of things, most commonly:
How Deposits work
Rescheduling, cancellations, or no-show policies
Whether or not they're accepting cover-ups
Policies are displayed on Artists CO:CREATE profiles, and right before you Book.
You'll need to review and agree to your Artist's policies right on CO:CREATE before you pay to Book with an Artist, to avoid surprises.