Claire was standing at an intersection waiting to cross the road. She saw John's car run a red light and hit a car driven by Walt. As the three of them waited for the police to arrive, John approached Claire and introduced himself, leaving a $100 bill in the palm of her hand after they shook hands. John then said, "There's another nine of them to follow if you don't act as a witness in court about this accident." Claire agreed, stating, "It's a deal," and slipped away from the accident scene. She later learned that the matter had been settled, and no charges had been brought against John since there were no witnesses to the accident. Claire contacted John to get the rest of her money, but he refused to pay her the remaining $900.

Claire wants to know if she can sue John for breach of contract - what would you tell her?