1. Ask directly: You can politely ask the waiter or cashier directly about the extra charge and ask them to explain the source of the charge.
2. Check the bill: Before closing the bill, carefully check the items and amounts listed on the bill to ensure that there are no extra expenses without your consent.
3. Communicate with relevant personnel: If you find unreasonable expenses, you can communicate with the manager or person in charge of the restaurant and explain your observations and doubts to them. Provide specific details and facts to support your claim.
4. Retain evidence: If possible, use bills or receipts as evidence for further communication or complaints with relevant parties in the future.
5. Complaint channels: If you can't solve the problem, you can seek complaint channels from restaurants or consumer protection organizations and report such misconduct to them.
It is important to remain calm and polite, and solve problems through proper communication. If your rights and interests are damaged, it is reasonable to insist on safeguarding your rights and interests.