Alfred Low asked:
In a S&P, the general accepted practice is 3% booking fee upon signing offer letter and 10% upon signing S&P within 14 days. Can the seller’s lawyer impose 10% upon signing offer letter and S&P within 7 days, if S&P not signed, 10% is forfeited?
Yes, the norm is an earnest deposit of 2-3% to be collected from the Purchaser and the balance of the 10% deposit to be paid concurrently with the signing of the Sale and Purchase Agreement (SPA).

The 14 days period to sign the SPA is a norm but it could also be 14 working days, 21 days or even 30 days depending on the bargaining position of the parties.

Whether the seller can impose any other terms as you have suggested is entirely based on the bargaining position of the parties.

Obviously, any deviation from the norm is at the risk of the party making that concession. It is a civil transaction after all that arms length deal operates on the basis of freedom of contract.