For the moment, at least, I’m resisting the urge to Google “MBW,” or “Mr. Brainwash,” because if I do then I’m afraid that I’ll find out that Exit Through the Gift Shop, the very amusing documentary about the contemporary art world, is an elaborate hoax, and I’d like to go on believing that Mr. Brainwash is real.

According to this film, MBW is the nom de art of Thierry Guetta, a Frenchman living in L.A. who at one point had both a video camera and too much time on his hands. He became altogether too taken with street art and street artists (this term refers to poster and stencil artists who plaster their creations on public walls, and not to graffiti makers who paint directly onto walls) and devotes his life to videoing their every move. For a time Shepard Fairey, the street artist who entered the mainstream with his iconic blue-and-white “Hope” portrait of Obama, is the star of the film.

And for some time the film seems to simply be a guerrilla documentary of a guerrilla art movement, of minor interest but little more to the non-fan.

But then Exit Through the Gift Shop morphs into something else altogether. Shepard Fairey is one thing, but for Guetta, the British art prankster Banksy is the great white whale. Not only are Banksy’s efforts, such as the beautifully ironic paintings he’s made on the Israeli-built wall in Gaza, genuinely dangerous to execute, but he, Banksy, is a master of anonymity. Guetta can’t get near him, and so, naturally, he becomes obsessed with finding him.

I guess it’s time for a word about Guetta. “Obsessed” is perhaps the nicest word to describe him, though some characters in the film prefer “retarded.” He simply lives to video his heroes.

The fact that he’s French, and about as impractical as it’s humanly possible to be, had me comparing him to Philippe Petit, the literal hero of Man on Wire, the great documentary about the French tightrope walker. Is the “French eccentric” a new documentary subgenre? I wondered. If so, I preferred the heroic Petit to the mere chronicler Guetta.

But then Banksy asks to see a draft of the street-art documentary that Guetta is supposed to be shooting, and the film finds a higher gear. Guetta is not a filmmaker at all, and his film is mere gibberish. So Banksy sends Guetta home to make some art of his own while he, Banksy, tries to re-edit the film. The idea, apparently, is that Guetta needs something to occupy his time, so why not make some art?

I hadn’t suspected that my leg was being pulled until this point. But when Guetta takes Banksy’s advice so enthusiastically that he goes on to become a new art star, pulling down thousands of dollars for his every sub-Warholian silkscreen, I wondered if the film might not be an elaborate hoax, a joke on the venality of the commercial art world, and on the gullibility of art buyers.

Banksy didn’t lose his anonymity in the making of this film, even though Exit Through the Gift Shop is credited as a “Banksy film.” He’s always shown with a hood pulled over his face and his voice is electronically modified. I started to wonder if he weren’t really Sacha Baron Cohen, and if we, the art house film crowd, weren’t his new marks.

Probably not. There is a real Thierry Guetta, aka Mr. Brainwash. He’s apparently designed the cover art for Madonna’s recent greatest hits collection. And I guess there really is a Banksy, though of course he could be a collective for all anyone knows. But still, by the end of this film you feel like you’ve been played. And that’s a good thing.

The art world is such an obvious target for satire that you have to approach it from a very oblique angle, tricking the viewer along the way, in order to make your point. The art world is venal. Duh!

But Banksy makes that very obvious point in a brilliantly amusing way. I hope he makes another film.