It is illegal, and rare, to charge a service fee without the customer's consent. But a tip of about 5% to 10%, depending on the type of service, is customary. For example, Germans usually tip their waiters but almost never the cashiers at big supermarkets. As a rule of thumb, the more personal the service, the more common it is to tip. Payments by card can include the tip too, but the tip is usually paid in cash when the card is handed over.