For those of you who have actual jobs in the real world, think about your work-life experiences. A few of you may be fortunate to love your jobs most of the time but most of us work for a living and the best we can hope for is not to hate our work.
In the course of a work week, you probably deal with a lot of different people. Some may be truly annoying but you put up with them because that's what you are paid to do. Others may be more fun to work with, and you probably look forward to working with them much more; some may even be your favorite customers, or clients, or colleagues (depending on your job).
Even so, most of the time, even our favorite work-friends are not as important to us as our "real" close personal friends and family.
You may want to consider that the personal feelings of an SP are not that much different. She may sincerely prefer some customers over others because they treat her more respectfully, ask less difficult things of her, or are simply better groomed and cleaner. However, it's unlikely (in most cases) that she really likes them better than her real friends.