Plus, the users are self segregated, what a dream.
Imagine you wanted to sell drop shipped backpacks. All you'd need to do is create and prime, or buy, a dozen or so accounts, and start recommending your own brand subtly in every recommendation thread in r/backpacks or whatever the most popular sub for it is.
People trust Reddit because they assume they're other real users. Many advertisers already know and take advantage of this. It's nearly impossible at this point to know who or what is authentic.
