Second Tier PPC Network - Advertiser Cannibalization

As I come to learn more about these networks, it is hard to see beyond the smoke and mirrors.  Maybe you already knew this, but publishers using these networks treat them as they do ad networks.  They leverage software so they so they can select which of several PPC network ads to accept based on CPC being bid.  So, the implication for me is that I can drive my own costs up if I choose to participate with more than one PPC vendor as an advertiser.  Of course all of this is far from transparent. 

If you have experience and best practices you want to share on this topic I welcome your comments.