They don't actually care to get the competitors' prices right. They find a "worst case" example somewhere and go with that, with tiny fine print saying something like "results not typical" or "results may vary based on location".

For example, Geico says "you could save up to $500". I don't even pay $500, but as long as they can show there was a single case where they saved someone $500 they're golden.

This

There are services out there that provide the info. I once used these guys: http://quadinfo.com/Pages/Default.aspx.