For me it's less about my knowledge vs. theirs, and more about get the fuck away from me and stop trying to make a sale.

They're like horseflies circling around your head repeatedly, even though you've politely shooed them away multiple times. There is a furniture/appliance chain in Canada called The Brick that is hands-down the worst offender for pushy salesmen. I haven't gone into one in years because every time I do I wind up wanting to scream and hurl an ottoman through the front window.

I firmly believe this is one of the main reasons retail is dying. I'm willing to pay the markup for the convenience of buying a product and having it in-hand today, but when I enter a mall and there are vultures on every corner trying to make small-talk and casually direct me to today's hot deals, I want nothing to do with it.