There certainly are marketing "gurus" who are nothing more than conmen. But skilled marketers also come across "founders" with nothing but a shitty MVP (or even just an idea), an inflated sense of their own ability, and grossly exaggerated expectations of the potential of their product to change the world, if only a marketer would "partner" with them to build a brand and traffic. It's a huge risk for a marketer to invest months of time in a product that could go nowhere because the founder is a flake or the engineering doesn't work out — all on commission with no stock options if everything comes together.