Disputes with buyers of art are often for less money than the maximum recoverable in small claims court. Since the small claims process is so cheap and easy, small claims actions therefore can give artists the ability to apply real pressure even if there is only few hundred dollars at stake.
Unfortunately, the fifty states vary considerably in what they allow to be sued over, where the suit must be brought, how much can be sued for, and how formal the process is. A few states require that the defendant be a state resident or have a place of business within the state. Also, you will not be able to sue for copyright infringement because that is a federal law and there is no such thing as a federal small claims court. Typically, you can sue only for a broken contract or, sometimes, a tort.