Just because you are a paying customer doesn't mean they have to put up with you being an a-hole (which I'm reading between the lines you were). being polite and friendly always gets you better service no matter where you go. You could also be proactive and call first, have them order the parts, and then go pick them up when they arrive.
That aside, if you don't like a dealer, go to a different one. I have a dealer 15mins away that I hate, the people are morons and they never have the right parts. I now drive a half hour to a better one with nicer, more knowledgable parts people, and a larger inventory. I suggest you do the same.