Legal Question in Business Law in California

In California, and most everywhere else, you don't get a "cooling off period" or any other right to cancel a contract within a certain time. Once you sign a contract you are bound and you are liable for breach of contract if you cancel it. You are lucky the guy is only asking you to reimburse him for the money he spent in reliance on having the contract. Legally he is also entitled to demand whatever profit he would have made as well.