What is the best general approach when refusing further service to a customer?

The best approach when refusing service is to remain calm, polite, and firm. The server should clearly but respectfully tell the customer that they cannot serve them any more alcohol, avoid arguing or being judgmental, and offer alternatives like water, food, or help arranging a ride. A non-confrontational tone reduces the chance of escalation. Being matter-of-fact and treating the customer with respect — while holding the decision firmly — is the most effective and safest way to handle the situation.