I'm assuming you spend a decent amount of money on AdWords campaigns or they wouldn't be offering this service in the first place, so it's really not FREE, it's value added customer service. With that said, never turn down anything if it doesn't cost extra because worse case they might do something you hadn't thought about and you'll learn something new. Whether the resulting work they do is suitable for your actual needs is another story altogether, but if it costs you nothing extra to find out what they want to do, then by all means, take advantage of the offer.
Whether you actually run that ad campaign or not is another story. :)