Updated that script for you: - I want to have a beer! - ok, scan this QR, and accept the transaction - there you go! - thank you, here are your 5 beers - o

Updated that script for you: - I want to have a beer! - ok, scan this QR, and accept the transaction - there you go! - thank you, here are your 5 beers - oh, did I just pay for 5? I wanted 1! can you refund me and take these back? - sure! can I see your QR code? - there you go! - thank you, here is your 1 beer and refund Note that I'm totally burnt on bitcoin for practical reasons, but your example is just silly.