China's a strange beast, though - that's a feudal economy with a market economy poorly welded on managed by a command economy and balanced out by a criminal economy. "Tipping" in that universe is a whole 'nuther custom. I'll bet you could learn a lot by studying "tipping" in China but you'd have to study things you wouldn't normally associate with the service sector. Delivery works like that. Consider: 1) I sit down at your table. The person that seated me gets a small part of your tips. That's contact (1). 2) The server comes by and brings menus and takes a drink order. That's contact (2). 3) The server returns with drinks and recites specials while also asking about appetizers. That's contact (3). 4) The server returns for a food order and may have to return again with a drink refill or if the customers need more time. That's contacts (4-6). 5) The server brings food and checks drinks. That's contacts (7-8). 6) The server checks at least once to see how the meal is. That's contact (9), maybe (10) if there are more drinks. 7) The server clears the table and asks about dessert. Contact (11-13) if there are desserts, coffee, drink refills. 8) Server clears the table again and brings the check. (14) 9) Server collects card. (15) 10) Server returns receipt. (16). That's up to 16 customer contacts. If the server is 25 feet from the kitchen, she's walking more than 100 yards carrying stuff exclusively for your use and she's doing it in livery with a smile on her face. Compare and contrast: you show up in your clothes, listening to your music, carrying a pizza. On the flip side, tipping gets stupid with wine. Why, exactly, is the sommelier entitled to $30 for selling me a $70 bottle of wine for $150? That said, in China, wait staff get paid shit even in nice restaurants and they don't get tipped at all.
Oddly, pizza doesn't have a clear 20% rule. A lot of folk give $1-2 no matter how many pies you deliver.