Thanks for your reply.
Well, you will need to check with your Daughter as to whether Contracts have been exchanged. I am guessing that there hasn't been an exchange of Contracts, because if there had been, both the Seller and the Buyer are legally bound to sell/buy the property on the agreed completion date, and the Buyer is not entitled to raise any further enquiries once Contracts have been exchanged.
If Contracts have not been exchanged, I'm afraid either party is free to walk away from the Sale/Purchase without compensating the other party. If this is the case, the Buyer is therefore entitled to withdraw from the transaction and your Daughter is back to square one. Likewise, if the Buyer asks for any reduction in the Price due to this outstanding issue, your Daughter is free not to agree to this and can also walk away.
It appears to me that the buyer is "playing the game" and is not very morally acceptable, but the fact that he works for the Estate Agent does not change my answer.
I hope this sets out the legal position for you.
I am sorry this is not the Answer you wer elooking for, but if I have assisted, I would be grateful if you could leave positive feedback.