Why are people like this?

I've been working at a specialty shoe running store for three years now, im also a runner. I love my job and everything. What ticks me off is how (caucasian) people are so freaking picky about everything you size them evaluate them, and answer a million questions and they always seem to find something wrong it can be the dumbest thing ever and it is still not enough. They always try to test your knowledge because " oh in the internet it says otherwise", okay then go order your shoes off the internet then! Seriously no other race of people are like this. So my question is why do caucasian people complain about dumb things? Nothing ever satisfy you people!