Lex Luthor had been arrested and convicted of fraud. He served a sentence of 5 years at a state prison. While in prison, he learned the laws of real estate and how to become a real estate agent. After being released from prison, Luthor tried to become a licensed real estate agent, but because of his fraud conviction, he was prevented from acquiring the license as required by state law. The cost of obtaining a real estate license is $250. Nevertheless, Luthor began to sell real estate as a real estate agent for a real estate brokerage firm under a false name. Luthor became extremely knowledgeable and skilled in representing families in the purchase and sale of residential real estate. The Kent family hired Luthor as their broker because they wanted to purchase a home. Luthor showed the Kents the home of their dreams and negotiated a very favorable price for them. However, two days before the closing of the sale of the home to the Kents, the Kents found out that Luthor was not licensed and had been a convicted felony, so the Kents refused to pay Luthor his commission. Luthor sued the Kents for breach of contract. What is the Kents' best argument in defense against Luthor's claim?