Final answer:
The best response to a difficult client who appears to be under the influence of drugs or alcohol is to politely ask the client to leave.
Step-by-step explanation:
The best response to a difficult client who appears to be under the influence of drugs or alcohol is to politely ask the client to leave. It is important to prioritize the safety and well-being of yourself and others in such situations. Engaging in a heated argument may escalate the situation, while offering the client more substances would be inappropriate and potentially harmful. If the situation becomes uncontrollable or dangerous, it may be necessary to call the police for assistance.