Generally speaking, it would depend upon the contract that you had with them. If there was no contract then you are likely out of luck. If there was a contract, the answer would likely be in there. I am both an attorney and a licensed real estate agent in the State of Texas.
If you have any questions, let me know. I can probably take a look at your contract with the clients and tell you if you have no case, a solid case or something in the middle.
Have you asked your broker for guidance? Consult with a qualified real estate attorney and provide them with ALL relevant facts and documents to determine if this is worth pursuing.
It depends on the language in the buyer's rep agreement, if there was one. If you did not have a buyer's rep agreement, then you are out of luck.
The above statements are provided as general information and not intended as legal advice. Each matter has its own set of unique circumstances that cannot be adequately addressed without consultation. You are strongly advised to hire an attorney licensed to practice law in your state to represent you.