Need to check with lawyer. But nowadays very common of seller backing out of sales.
Alot of buyers just pass the cheque to the agent to secure the deal, machiam me
So, what happened from my experience was, the buyer accepted the cheque but didnt cash it, and return the cheque and back out of the deal. I'm not aware if there is a signed agreeement between the agent and the seller though.
Unless your case has a signed agreement, dont think there's a case, and of cos all the hassel of going thru it.