Let me play devil's advocate here for a second....
While Buzzsaw's solution is sub-optimal and in fact I thought it was horrible at first glance, it is not THAT bad in practice and it could work.
With books available at ratings higher than "C", how many new players will this book be able to signup? It would seem that being able to get the "stiffed" players paid would outweigh the potential cost of new player signups. No offense to Buzzsaw but really, how influential is his site in terms of attracting new players to a book especially a "C" book. I could see this trade working out.
Just a few suggestions/notes (btw, I've never been to SBR's site but I will tonight given the recent activity offshore)......
1)Buzzsaw, have you considered an S&P type announcement where you say the book is being considered for an "Upgrade" to say "C" and you remove the current rating?
2)Does your site allow the user to look at the "Ratings History" for a book?
I would think that the terrorists...I mean books...would find those suggestions sort of attractive and it would help you eliminate this conflict issue.
IMHO, I don't think I could have made the decision that you did. It reeks of a situation where the book, you, and the "stiffees" will get some benefit at the expense of new post-up players who may not know the risk they face with the book. Agreeing to a "C" puts your ratings integrity at risk.