Maybe I'm asking the question incorrectly then. I know that there are programs that are more aggressive in how they search for results. There are programs that click through paid result (ack, click fraud) and organic results to make sure that you actually get to the destination URL. Why not list them? What with all of the anti-link buying messaging that Google puts out, why not list the most popular link buying company?
Karl, from your own experience, do you have periodically re-program how your service checks rankings? I.E. looking for tokens and such in the HTML to begin/end reading sections and what not?