This type of thing (scan QR code) is how basically all payments were done when I was recently in China, via wechat or alipay (either you show your QR code for big shops, or scan their QR code for small shops / vendors. They can just print them out if they want and hang a copy).

I found it superior to other systems I've used in basically every way. Particularly for small market stalls -- I scan their QR code, I enter how much I want to send them. They never get my details, I don't have to trust they didn't fat-finger the price. It also makes it amazingly easy to send money to friends, just scan their code and send them their share of dinner.