advertising vs sales

Are you in advertising or sales?

I ask myself that a lot. I wonder if there is a difference at all. So, when my brother-in-law told me he was going in to print sales I thought he'll be great. He's a great sales man. He's talked me in to many things that I haven't regretted but wouldn't have done without him pointing out the clear benefits and explained the risk/reward of the situation at hand.

He can sell.

I guess the thing that has me pondering his success would be whether he knows the advertising business well enough and, honestly, does it really matter if you do or don't?

Is there a benefit we can weigh or measure that can prove whether or not a person with a strong background in advertising has any advantage over somebody that is just damn good in sales?

Does it matter if you know ad giant, TBWA, is responsible for the 20+ years of historic Absolut ads?