I'm pretty sure that it's TPTB at whatever Big Corporate Entity® that approve the tie-in novels. Joss would never allow such tripe to be published using his characters. I have read two Buffy/Angel tie-in novels, and both of them (by two different authors) sucked rocks. The writing was flat, the characterization was off, and the plots were predictable.

I don't just "think" I can do a better job, I *know* I can. If that makes me an arrogant bitch, I don't care.