Very easy to post things on Reddit as a marketer, particularly when working with a small group who can respond to each other to season threads. Plus you can pay trusted Reddit account holders to post items for you.
A great marketing tactic is to pose as reddit users. If you have just 2-3 realistic accounts, you can ask a question as account 1, and write your answer with account 2. Now imagine a company with $$$. They can guide an entire thread.
I'm sure there are marketers on Reddit, but the nature of virality itself makes it pretty robust against attempts at manipulation.
(You have to astroturf really hard or be a part of an existing wave, astroturfing reads different, so the best you can hope for is bending the narrative a step or two)
now imagine entire countries spreading influence and manipulation through reddit. add in extreme bias and hivemind. only a select few topics where reddit would be a good place to learn from