Is there any penalty that you can impose upon a home buyer who goes beyond their closing date?

The contract that we signed with our potential home buyer indicated that they had to close on our house by 9-29. To date they have not done so. We signed a paper giving them an extension until 10-6, which is tomorrow. They are still not ready to close. They do have a commitment letter from their lender, but their lender has yet to send a ';packet'; to the title company for the buyer to sign off on. Are we just at their mercy and have to continue to extend the contract for them? They keep saying that once the packet is recieved by the title company they will overnight it to the buyer and the buyer will overnight it back and then we can close. This has been the story since the 29th. Any ideas on what the hold up could be? Is there a penalty that we can make them pay since they are still wanting to close and have yet to do so? We are incurring more daily interest on the loan for each day they go over on the closing. HELP!!!