Legal Question in Real Estate Law in California

Based upon your zip code, I presume you do not reside in California, so filing suit in Small Claims Court here would be too expensive unless yo were planning a tip out here again. If you have pictures and/or statements from others who saw the problems, you send a copy to the owner and say if he had been the renter would he not want a refund? You likely will get no result. You could rate him on the web site where you found the house, if the site is set up for that, report him to the local BBB and health department for the mold and blood, etc. Do not threaten to do so unless he reimburses you as that might be considered extortion. If the check has not yet been cashed, which is very unlikely, you could stop payment on it.