What evidence is there for each side of the debate over the authenticity of "Exit Through The Gift Shop"?

Wikipedia's entry has a nice summary on the speculations:

The film received overwhelmingly positive reviews, holding 96% on
Rotten Tomatoes, and was nominated for Best Documentary in the 2011
Academy Awards.[5][6] One consistent theme in the reviews was the
authenticity of the film: Was the film just an elaborate ruse on
Banksy's part, or did Guetta really evolve into Mr. Brainwash
overnight? The Boston Globe movie reviewer Ty Burr found it to be
quite entertaining and awarded it four stars. He dismissed the notion
of the film being a "put on" saying "I’m not buying it; for one thing,
this story’s too good, too weirdly rich, to be made up. For another,
the movie’s gently amused scorn lands on everyone."[7] Roger Ebert
gave it 3.5 stars out of 4, starting his review saying that "The
widespread speculation that Exit Through the Gift Shop is a hoax only
adds to its fascination."[8] However, in an interview with
SuicideGirls,[9] filmmakers Jaimie D'Cruz and Chris King denied that
it was a hoax, and expressed their growing frustration with the
speculation that it was: "For a while we all thought that was quite
funny, but it went on for so long. It was a bit disappointing when it
became basically accepted as fact, that it was all just a silly hoax
... I felt it was a shame that the whole thing was going to be
dismissed like that really - because we knew it was true."[10]

The New York Times movie reviewer Jeannette Catsoulis wrote that the
film could be a new subgenre, a "prankumentary".[11]

New York Film Critics Online bestowed its Best Documentary Award on
the film in 2010. French journalist Marjolaine Gout gave it 4 stars
out of 5, linking Mr. Brainwash and Jeff Koons and criticizing Thierry
Guetta's art as toilet papering.[12]