People have attempted to auction off actual walls he's painted.
Recently, two murals which had been physically removed from the buildings they were painted on were brought to auction at the Fine Art Auctions Miami. Though Banksy did not give consent for these murals to be removed and sold, it was within the seller's legal rights. The murals included Banksy's Wet Dog splatter painting from Palestine and his Slave Labor piece in London, put up in 2012 around the time of Queen Elizabeth's Diamond Jubilee, celebrating her 60th year on the throne. The piece was put on a store occupied by the Poundland chain, who had recently been the center of controversy when people discovered that Poundland profited off of goods produced through child labor. The murals each had an estimated value of about $500,000-$800,000. The public outcry over this controversy led the auction house to pull the two pieces from the auction at the last minute. The Slave Labor piece was later sold privately for $1.1 million at auction in London.
fact via / image via (photographed by: Deptford Jon)