Rude clients are an annoyance!
I have to go and visit customer sites to quote for installation work regularly - some are as nice as pie (and it isn't just down to the coffee!) and some are stand-offish and disinterested (even though you may be subsequently spending tens of thousands of their cash). It costs nothing to be pleasant and those customers who've made me feel welcome always get seen to first subsequently - if I'm passing and they have a problem I pop in that day and fix it for free - but the rude ones....! They can wait!
You get the best out of people when you treat them well. I may be the hired help but don't behave like I'm a servant!