What confirmed it for me

Was not so much that BDJ is too well written to be real (I was convinced it was Martin Amis or some other bloke from the beginning). No, the final confirmation was the way she reacted to the various newspaper stories, like the one in the Times. She talked about the Times article as if all her readers would know what she was on about. Which confirmed that her real target audience is literary and media London.

Besides, she couldn't keep up the style, and it all started to get very Luvvie and Darling, so it's not even as if it's written by the same character any more. Shame. To really get my respect, they should have kept it up for years.