Where the service is the sale of a property or a business, then the agent's selling fee is paid at settlement.
Where settlement is defined as the legal entitlement to the property passing from the owner to the buyer, or upon the buyer taking possession of the property.
Where the service relates to the management of property, the agreed fees are normally paid monthly.
If it is an off-the-plan sale, then the developer and agent may agree to payment prior to settlement.