How many types of customers are there according to the speaker?

(W: )As a waitress,I see a lot of differences in the tips my customers give me. The worst kind of customers are those who are the most impatient people to serve, and then, they leave me nothing. A step above them is the second type of customers who must think they are great tippers. If they order a five-dollar-ninety-five beer, I’ 11 get six dollars and be told to keep the change. Even so, these customers let me know they expect quick service. The next type are those who leave the normal fifteen percent tip. They are often quiet and orderly. These people are always welcome, especially after I’ ve dealt with the other two types. But in the last type, I find my waitress’ dream come true. These customers order a five-dollar-ninety-five beer and pay eight dollars with a cheerful "Keep the change", even if the beer happens to come through slowly. To make things even nicer, these customers order the rest of the evening, adding big tips every time. The variety makes my job interesting, but I have to admit that I like the last two types best.