civil vs. criminal suit

This is an oversimplified hypothetical situation. If P sells products to D and D does not pay, P can sue D for breach of contract. If P and D are in different states, the federal court will have jurisdiction.

Fraud is a criminal act defined by statutes. A private person cannot bring criminal prosecution. It is the job of the government (district attorney).

What claim should be filed in which court by whom depends on the facts of the case. The oversimplified discussion is only about the hypothetical situation.