When banner ads are displayed on most websites (ecommerce sites, internet forums, article pages, free email inboxes, etc.), are advertisers charged per click, or per impression (CPM)? What's the norm?
There are a wide variety of both type of programs around. I don't think there is any norm. CPM programs are as popular as PPC. It's more a matter of working out which suits your business model best.
PPC is mostly someone use it to get unique click which the traffic maybe higher conversion rate. But this mostly is expensive. CPM is charge in impression. It cheap but you do not know how much you click you get before develop and you only can estimate it. Mostly people use CPM to burn their impression to create brand awareness. I still prefer banner go with CPA which it charges in a fix price per quarter or per month?