If a seller omitted or lied in the seller disclosure?

and i can prove that they knew or didn't do what they were supposed to do, what is the proper recourse? one of the issues is if you did additions to the home without proper permits, the seller said no. i went to the appraiser to get an exemption and saw the layout of the house and saw that there was an old plan without the three added rooms and she was being taxed at the old rate. i'm thinking about the tax consequences and i'm not getting busted for that! i know have to seek legal advice, but i have a case, right?