Paying commision after S & P? Your agent is really cannot wait!
Although you are suppose to pay them the commision but your transaction has not complete yet! Usually after you sign your S & P (I meant the formal one at your lawyer office, and this is a legal document that both parties must complete the transaction), it would still take almost 1 month to register the transaction, only then your S & P transaction is compete. Meanwhile, there could be little things that come up and you would need your agent to help, so I would not pay them until the transaction is fully complete.
Mind you, the only way that they can sue you for the commision is go to the small claim court and that would takes time as well, so you can talk to your agent about it to avoid misunderstanding.
Sorry to say, I think all agents are the same in HK, after you sign for the paper, all they care for is the commision now. The earlier you pay them, the less service you can get from them unless they know that you would have repeat business with them!