How do Business work together with Marketing agencies to ensure the campaign they're trying to market will be perfect?

those marketing agencies are also business.

I think I know what you are asking, in most cases the marketers will bring a product to the market and merchandise it as they wish. Having said that many companies hold the right o approve any advertisement that brings their product to the fore front. Usually they want to make sure that the product isn't misrepresented to the public. An example of this was shortly after Smokey and the bandit was released some advertisers were trying to sell the Pontiac like the Bandit drove and young folks would buy the car and wanted it to do what they saw it do in the movie and what it was advertised to do on TV. General Motors stopped this very quickly

As for the advertising that the business does, it isn't referred to as a marketer but is called public relations more common it is called PR