Carrier's testimony is very interesting. I think I am not wrong in demanding strong evidence for claims of this sort of fraud. I could, I think, figure out if there is any sign of Flew's philosophical intellect behind the various parts of the book, though I don't publish on the specific arguments. Carrier actually casts doubt on Varghese's claim that Flew approved ten drafts. A philosopher like Swinburne or Robin Collins, who actually present and defend the type of argument Flew uses, would be the best people to be able to tell if these arguments showed some philosophical competence.
If Carrier et al are right, then this book is profoundly tragic. Tragic in virtue of the fact that an honest account of Flew's mental development throughout his career would have been valuable. And tragic that a couple of unscrupulous Christians damaged the credibility of their own faith by passing off their own poor arguments onto a paragon of intellectual honesty. If that's what they did, these guys should be horsewhipped. It does bother me that apparently the book does not delineate the remaining, very important, differences between Flew's own view and orthodox Christianity.
It would be good if Habermas, in his own voice, or Douglas Geivett, who has corresponded with Flew extensively, could say something.
In any event, I would not have expected a cutting edge defense of theistic arguments from Flew at this stage of his life, so the fact that he doesn't provide that would prove fraud. I would have hoped for a sense of his thinking across his career and some idea of what kinds of arguments moved him away from his lifelong atheism. It does seem that the autobiographical stuff has a lot of Flew content.
Please don't take these comments as the final verdict from me. I would have to read it to form my own final opinion, or get the opinion of, as I indicated, people like Swinburne.