This is was of those awesome things that happens in the world once in a while, who would have expected this and the faces on people watching.
I think it is obvious that Banksy does not need the money and ingenuity to get this through to auction with a shredder built into the with obviously a battery and some sort of remote trigger device.
I think what these say is f*** you art world for these stupid prices for a bit of paper and paint.
Artwork by U.K.-based graffiti artist Banksy went through a shredder moments after it sold at auction for $1.4 million US.
— Read on www.cbc.ca/news/entertainment/banksy-girl-with-balloon-auction-1.4853419
The Retired Dude 
I read about this today. I think that was a fabulous idea!