Astroturfing as in hopping into a group and creating a post promoting your product? Have you ever seen that actually work?

Almost every subreddit I see bans any kind of promotion and even posting of links.

The number of pictures that are actually just ads upvoted to the front page was absolutely astonishing when I used reddit. I didn't understand how people could see a Coke can with a funny name on it and not realize that was an advertisement.