Isn't the act of tipping a charitable donation? Watch
Yes really, waiters are figuratively begging, in the form of smiling and greeting and serving, to earn an extra buck.
A rule that should be applied without incentive when dealing with clients.
Whether the customer pays a tip or not is something done under their own free will,the waiter/waitress is not forcing nor are they begging them for a tip.
There is a difference between begging and receiving a tip!