There are some trades where tips are common place,Waitress,taxi driver,coach driver,hotels etc.
Since I am in the 'Tip category' i always tip the above.
Without bragging I'm a very friendly taxi driver with lot's of regulars,I have pop quizzes on journeys,go shopping for some etc.
People get more than just an A-B and appreciate good service.
Make them feel special like they are your most important customer and you get rewarded.