What is a seller backs out of the contract for property sale?

Assuming that the contract was delivered to you after the seller signed, doesn't give the seller the right to back out of the contract within a given period of time, and that the seller has no valid reason for backing out (e.g. some breach by the buyer), the seller has breached the contract.  As the buyer, you can (a) file a lis pendens against the real property which was the subject of the sale, preventing the seller from selling it to anyone else pending the resolution of the lawsuit between the seller and you (I assume that this was a contract for the sale of real property) and (b) sue the seller to either (your choice) compel the seller to perform the contract and sell the property to you on the contracted for terms or for any damages you have suffered as a result of the breach.