I got one of those calls a few months ago and I called back, I told them I had just bought a brand new car that month, and based on that I was pretty sure my warranty was NOT expired and wouldn't be for the next 50,000 miles. The caller person just went "Oh. Okay." and I haven't gotten any calls anymore.
Just a small friendly suggestion. Would it be possible that you guys make the link go to the quiz *itself*? It's a little annoying to go through another link in the mental floss website to get to the actual content.