So I've always had an interest in paid advertising, with a few forays here and there. However after reading some IM journeys I started to see somewhat of a pattern in facebook posts, where the author would use pay per conversion. Now it seems like that would be the best bar none as you would only ever have to pay when you sell something. However if that is the case what is the point of doing things like Pay Per Click if you have guaranteed profit from that? I know I must be missing something but for the life of me I can't figure out what.