By extension, high-karma accounts that are run by marketing companies can post in a niche subreddit to subtly promote their product or disparage their competition, and they'll end up on the front page of that subreddit. They'll get a lot of views and a lot more engagement than the average unsophisticated user's post would -- and those astroturfed posts would, on average, rank higher in searches.

This is analogous to SEO, but rather more insidious and sneaky. You can spot SEO blogspam from a mile away. You don't know if a Reddit user is a real person, a bot, or a company's representative.