So there are a few different kinds of display ad networks out there. This would include: general banner ad networks, advanced targeting ad networks, and exchanges.
The Ad Network world is certainly in a state of flux and these definitions are changing – but the general banner ad networks business model concentrates on performance type CPA (DR) offers. What this means is that they serve a whole lot of ads with a whole lot of offers for “Free Florida Vacations”. These networks are shall we say more liberal with the types of advertisers and publishers they work with.
The advanced targeting networks business model concentrates on highly targeted Brand type offers. This type of network generally offers very high CPM (high for remnant at least) but lower fill since they are only able to monetize qualified traffic. These networks generally are more restrictive in terms of the advertisers and publishers they work with because they need to be to work with premium partners to command premium rates.
The exchange is where all these networks collide; and indeed most all ad networks participate in some way with exchanges be it with MSN, RightMedia, and/or DoubleClick. It is in this marketplace where premium ad networks can be exposed to the more flexible policies of the general banner ad networks if they are buying and selling inventory. This issue is much worse when it is the exchange in questions policy not to provide adequate transparency between the advertiser, network, and publishers partners.