I must say Good Service Attitude and Manner is the major factor.
This afternoon when I visited a girl in HB-B, may be because I was too tired after a non-stop working whole night for chasing the deadline, I was unable to keep my young brother in good condition for ML. That girl immediately show impatient and tried to use hand to let my sperm out. When I stopped her and asked her to use her mouth to seduce me, but her whole person's expression showed she dislike doing so. After I washed myself, she dared to ask for tips!!!
I simply told her that her service attitude was really worse, and I told her to think about if she want to earn sufficient money in order to leave the present job, she had to improve her attitude.