No Evidence for Marketing

 If marketing worked, you should be able to go onto youtube or webnovel sites, go downmarket, and find gems that have bad marketing. You can't, though. If you have a spare-spare afternoon, try it yourself. Go way down the pagination.

 Win win. Either I'm right and you find nothing, or I'm wrong and you can point out a hidden gem for me. 

 It is true that bad things can get good ratings. However, whether this is due to sharp marketing or sheer stochastic noise looks, at first, like an open question. Then you realize it's corruption. Someone has their thumb on the scale. Baits in conformists.

 Marketing with no obvious flaws regularly fails, and many popular things have hilariously bad marketing. If something is having an effect on apparent ratings, it's corruption. E.g. the NYT 'bestseller' list is editorial, as per court rulings. It's not based on anything silly like sales, especially not sales to folk buying the book for themselves with their own money.

 The best marketing by far is having a quality product. Thomas Kinkaid was not poor. Despite suffering explicit suppression. Although there is upmarket trash, there is no downmarket gold. 

 There is no such thing as bad publicity because there is no such thing as good publicity. I expect it's a wealth-cap thing. Either the author has spare wealth capacity, or they don't. Publicity is irrelevant. It's likely that publisher contracts, or going indie, paywalls, incentives, subscriptions - none of it matters. If you can get paid, you get paid.

 Quality is the best marketing, providing the market has demand for it, anyway. Quality up against no demand is meaningless. Regardless of how amazing your venusian habitat is, nobody can get to venus. Doesn't matter how good your logic is if nobody else (public) is capable of logic. ¯\_(ツ)_/¯