Many subreddits automatically delete posts or comments from users with low karma. Also people trust users with older accounts and a good amount of karma more than new users or people with low karma.
Keep in mind this is either a subreddit or Automoderator setting.
Subs can limit posts to users with some minimal karma or age. Typically this still permits comment, though harvesting comment karma is then incentivised.
Automoderator, a rule-driven automated moderation tool, can actively interact with posts and comments based on various criteria, including automatically holding or removing posts or comments, messaging submitters, and other actions. This is heavily used on highly-active subs, and pretty well documented.
The power users do, moderators do, those obsessed with reposters and bots too but I don't think the majority cares enough to check that. Most just follow the initial votes, so if the users who were early decided it was worth upvoting the rest of the people will generally just follow along. I think that's why selling votes is also profitable, you can get your post to the frontpage if it is good enough and you bought a few hundred early upvotes.
Subs can limit posts to users with some minimal karma or age. Typically this still permits comment, though harvesting comment karma is then incentivised.
Automoderator, a rule-driven automated moderation tool, can actively interact with posts and comments based on various criteria, including automatically holding or removing posts or comments, messaging submitters, and other actions. This is heavily used on highly-active subs, and pretty well documented.