Behodar:A bit like when you go into a shop and can't find an X. "Do you have an X?" you ask. "Why do you want it?" comes the response. They get all indignant when you reply "I want to buy it"!
That response actually makes sense, if it's a slightly oddball item or something that people frequently get wrong ("Do you have a huge screwdriver? I need it to hammer in a nail") they can suggest an alternative or better option. That's exactly why you go to Mitre 10 and ask the older retired-builder types for something rather than the just-out-of-school kids, the kids will tell you they don't have that, the experienced guys will ask what you're trying to do and a lot of the time come up with a much better and/or cheaper approach than your one.