Banksy's art value is context dependant -- graffiti vs. canvas.
How many people might have recognized the art but assumed it was just plagerized (term for copying art vs. text?) to sell on the street.
I know Banksy, but had I been walking down that street and saw that kiosk, I would have assumed it was just some hack copying Banksy's style, on canvas, to make a quick buck on the street. Like buying a Rolex on the sidewalk. I would pay $60 for signed and provable Banksy art. But no more than that for canvas art. He isn't known for canvas art.
If I had a building with a blank wall, I'd invite and even pay a sizable amount for Banksy to paint on it.
Bullgrit