Is paid traffic really worth the money ?

There is somethine that bugs me for a while. I've been considering buying traffic from traffic sellers, but it is really worth the bucks spent ? Has anyone had decent conversion rate from paid traffic ?
Besides, I'm basically like this:

I mean if they're able to send you 100K "real adsense safe visitors" a day, why don't they use it for themselves ? Won't it bring them more money instead of selling it for $30 ?

See original post by tobalsan