I don't really agree with your idea either. Another way to look at pay-per-post campaigns is that participants aren't required to meet a certain post threshold per week or month. If a user participates in a paid per post campaign with no post requirements, then there's no pressure on them to meet minimum post counts every week or month. On the flipside, if users are forced to make a certain number of posts for their campaign, and they don't usually make that many posts, chances are good they'll start posting crap posts just to get paid for their posts and meet campaign minimum requirements.