Your may need to consult an attorney to see if you have any cause of action against the agent.
Depending on the nature of your contract, it is possible that your agent violated ethical Realtor guidelines. Your agent may be subject to a complaint to the state real estate licensing authority.
It also may be that your agent is also a victim of the buyer who entered into a contract on which they could not perform.
What proof did you have that the buyer could pay cash?
Not enough details to know. Also, review of your contract and your complaint by your agentâ€™s broker is a must. Again, you may be a candidate for legal advice.