Is there an issue of "face"? They lose face if they give in to what you want and not what they want for you? Or they lose face if the customer tells them what to do/provide instead of being the one in charge to decide?
It's very difficult for me to be pushy... at least in a polite way, and I feel it turns out the worst of me as I just get angry and grumpy at them. I guess I've got to learn... And I really don't feel like I have the energy/patience to have these sort of stupid conversations with people when I just need to get things taken care of. Like "I don't like how this bra sits." "No no no no, that cause cancer like that!" "No, I know how I want a bra to feel and I doubt you are really up to date on the latest research about cancer and bras..." ... Never mind the PHYSICAL pushiness in this case!