At least at one company, female client service representatives get lower scores from their clients even when they perform better than men and have more experience.
Larry Kim, founder of internet marketing company WordStream, recently analyzed about 300 responses from the company’s clients to a request to rate their level of satisfaction with their client service representative at his company on a scale of one to four. He found that all of the men on staff had above average scores, while all women had below average scores. “In fact, the lowest scoring male rep rated higher than the highest scoring female rep!” he wrote in a post about his findings.
Kim also found that the pattern favoring male client service reps was stronger among female clients than male clients, though both rated men higher.
Larry Kim's blog gives more information about the study. What's a bit tricky about it is the total number of client service representatives: nine, as far as I can tell. Nine is a small number and individual personalities can affect the results. Another tricky bit is the way Kim measures performance of an account, as a measure of the performance of the client service representatives. As he notes himself, the performance of the accounts depends mostly on the clients themselves (though it's also true that "customer satisfaction" can depend on diffuse and hard-to-quantify items, including the gender of the representative).
Nevertheless, it's useful to note that the female client service representatives had accounts which did better than the accounts of the male service representatives, and that most of the difference in the satisfaction evaluations came from the middling accounts, those that fell in the middle of their performance.
All that is to say that I'm not sure how conclusive this study can be. But it reminds us of a particular type of discrimination in economic theory: Customer discrimination. If customers prefer men over women or whites over blacks, on average, the preferred group will do better over time, will get more raises and more promotions and more business in general.