The version of ‘Girl With Balloon’ which was ‘destroyed’ at auction on the 5th October 2018 was put into auction at Sotheby’s by its then owner. Banksy gave the work to that owner so he couldn’t prevent this from happening.
I’m not convinced at all that Banksy didn’t want it to go into auction. The shredding event has greatly increased his notoriety and so far has boosted the market value of all his work. Sotheby’s sold three more works by him the very next day in fact, all at prices far exceeding their estimates. Without doubt Banksy will be collecting around £25,000 in Artist’s Resale Rights just for these four auction sales alone.
In keeping with his anti-establishment / anti-capitalism stance (just so much empty posturing if you ask me) Banksy doesn’t sell his new works anymore:
But of course he doesn’t need to. He can make a nice living from his intellectual property rights alone.