In California, contracts for purchase of real property must be in writing to avoid application of the statute of frauds. Also, generally, contracts for sale of real estate have deeds of trust and promissory notes which have provisions for default. You should consult a lawyer in your state to evaluate your rights and remedies.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.