Funny how Banksy, who was anti commercial things before as a street artist, now is obviously very torn being selling out and not. He is still selling out with this sale, but couldn't stop himself from trolling the buyer.
I feel like I'd feel in a similar way - hard not to sell when so much money is in play.
If the buyer wasn't aware of this prior to buying it then technically Banksy ruined the buyers art, or the buy can back out because he's not getting what he paid for.
Of course early believers were going to criticize him as a sell out, but Banksy's message and its embedded criticism of modern capitalism become even more powerful when monetized.
His art mocks and attacks the principles of a materialistic modern society, but strangely this makes it more attractive and valuable to that same society; this can only be described as an absurd and paradoxical logic. An example of their stupidity. The final irony.