But what if (hypothetically) you bought the printer and turns out printer has a sim in it that sends every single print job via cellular n/w to server.
Don't buy printers on the black market. Get a signal jammer. Built a Faraday cage.
Of course it is impossible but if it does happen Or say someone randomly writes a key and it happens to be your wallet. Who is at fault?
Arguing about impossible scenarios is pointless. If a randomly generated private key wouldn't be safe, there would be no Bitcoin.
Point is to our knowledge, we followed all the steps securely.
My point is a simple Google search would have been enough to know it's compromised.