First of all, it goes without saying that you should have used a professional (called a "Realtor") in order to avoid this type of situation. Did the Seller use a Realtor? I would guess not based on the context of your question. So besides not using a professional you apparently also did not do your "due diligence" in ordering inspections on the property during your inspection period. This would include at a minimum Pest, Property and Natural Hazard Disclosure plus (based on the aforementioned findings or concerns) Roof, Foundation, Furnace, A/C, Mold, County Permits etc.
Did you use official California Assn.. of Realtor forms (the answer should be no unless the Seller used a Realtor). Did you use an attorney to close the transaction and insure all the paperwork was complete if no? How many forms and disclosures (on both sides) were not completed and therefore possibly making the entire transaction "voidable" in court?? My professional answer is consult an attorney. My personal answer is unless the items you refer to are considered Health, Structure or Safety AND amount to more than a few thousand dollars AND if you would have known about them you would NOT have bought the property at any price then suck it up, pay the piper and next time don't let greed get ahead of using a professional. Unless of course you are the kind of person who does all the work on your own cars, does your own dental work in the mirroe or takes out your kids appendix with a Dremel tool and duct tape.
There is an old adage in the real estate business. It is obviously still true. "Buyers are liars and Sellers are story tellers". I was told this on day one and it is proven almost daily.
@ Annette Lawrence, RIGHT ON!