First, I want to say I'm 3 days late in getting to this post due to TypePad being down all day yesterday, and initially waiting for updated information from traditional Ad Agency Associations for this post.
So, that said, I'd like to repeat what I said in Part II of this series: "Traditional Advertising Agencies have been around a lot longer than 10 years (the age of the Search Marketing Industry), and have much more complicated and less easily accountable media than just the Internet to deal with." For example, in the Institute of Communications and Advertising's (ICA) "Client/Agency Evaluation Guide to Best Practice with Evaluation Formats" it says on page 13 that traditional ad agencies are responsible for a performance evaluation on Account Management, Creative, Consumer Planning/Research, Production, Media Panning & Buying, Direct/Relationship Marketing, Interactive, Public Relations, Budget and Financial, and Agency Management.
When you consider the number of different types of media and the brand management responsibilities involved, it is hard for me to see how "Performance-Based Pricing" or "Payment By Results" (PBR) as the ICA calls it can be a truly "win-win" situation, especially in the first year of the agency-client relationship. This is true in the first year, because outside of internet web analytics, many of the "accountability metrics" used to determine specific remuneration feedback (especially as it relates to "Branding") are not as measurably definitive and instantaneous as good web analytics, in my opinion.
But, nevertheless, the ICA has specific parameters for their "PBR2: Advertising Agency Remuneration Best Practices", which includes a definition that says maybe only "some part" of the remuneration is PBR. It's free to non-members, so when you click on "Available Online" it eventually takes you to the PBR2 9/01 Report. On page 6, the history and benefits are interesting and applicable to SEO remuneration, in my opinion.