I didn't "pay" for a prep service...

***HOWEVER, I have helped a few buds go over the prep courses they paid for and practiced TMAAT questions with them A LOT. By the end of a few months, I felt very prepared and confident. I also took the advice from an HR friend of mine and videotaped several TMAAT events with my friend. That was huge for picking out little mannerisms and annoying "uh and you know" and poor eye contact.
I also had the fortune of interviewing with a 747/767 cargo company and a crappy airbus operator(strictly for practice, knowing full well I'd never leave my current job for them-Still have an open offer) NOTHING beats actual interview experience, if you can get it! (especially if it ends up positive)