Legal Question in Landlord & Tenant Law in California

You are following the law. To be extra safe, within 21 days of his telling you of the change in mind, send him a registered letter stating that he gave you $x as a security deposit and you gave him that full sum back on , and that he gave you $Y on as first month's rent and you told him that under the lease he signed he is liable for the rent for thirty days from the date he told you he did not want to go through, plus the days you took it off thee market because he gave you a rental check and signed the lease, but that you are attempting to mitigate damages byre-renting ASAP and once you have a tenant in and it is clear that they will be staying and paying the rent, you will refund the prorate amount.

Mr. Shers is right but leaves out an important detail. In order to charge rent until you get a new tenant in, YOU, not the defaulting prospective tenant, must take all commercially reasonable steps to find a new tenant. If you fail to do so, you are not entitled to collect rent from the defaulting prospective tenant.