Thierry is a Great Business Man (Banksy doesn't exist)
Thierry was so obsessed to meet Banksy that having no success in that due to his elusive identity, he went on creating him. Think about it:
What proof we really have that Banksy is truly Banksy? His studio in London? Well, that might just be a stage. Who works in the movie industry (or really anyone that watches movie) knows that everything can be created and made it look real.
We see a Banksy's exhibition. Yeah, perhaps that was a real one where Thierry just happened to be around.
Banksy's identity is unknown, so how can you prove that Banksy is in the movie at all?
It is clear from the movie that Thierry might not be such an artistic talent but he is a GREAT business man. Have you, like me, kept wondering how Thierry could afford just flying around following artists and apparently doing just that? He owns a successful clothing shop. He set up an art gallery and managed to have profit for 1 million dollars. He has a great sense of business. Think about this: he knows how to make thousands dollars out of 50$ cloths. He is able to arrange an art gallery out of garbage and other people's work. Now, do you think that Thierry would give all of his footage to Banksy and allow other people to spot an opportunity for making good money by letting them use his material?
Here is another conspiracy theory for you (in which, just to be clear, I don't believe): This movie is another great product by the money-making and opportunist Thierry Guetta. Banksy has nothing to do with it and Thierry is just fooling you around. He is a smart man and knows exactly what he wants and how to manage people. You see that towards the end where with all the stress for the opening event, him not even able to walk, Thierry shows us his authority and clearly tells his collaborators (not literally quoting): "Now you listen to me. I run this thing here. I want you to do this, this and that"
The point is that you can make up whatever conspiracy theory you want, but if you don't present evidences, you are talking of "fried air" (do you have this saying in English?)
The conclusion?
This is a great documentary and whether you want to call it mockumentary, prankumentary or conspimentary, that doesn't really matter. While watching some street art pieces shown in the film, it occurred many times to me thinking:"Wow, that's very good!"
It's an enjoyable documentary and many observations made so far are overall true whether you believe this film is a hoax or not: the commercialization of art, the struggle of real artists, the idiocy of the mass that just fall for the hype, art dealers that care more about the money they can make than the art itself, etc.