The answer is they don't do that - and they do it the other way around. The user shows THEIR QR code to the merchant (or automated kiosk).
Which means they still need a terminal - and it's going to be slower than NFC.
And NFC works when my battery dies.
Some merchants, like street merchants or drivers, will simply have their code printed out. You scan it and pay them and they get a notification on their phone or tablet that you've paid. Other places, like at bigger restaurants, have QR screen readers that will scan the purchaser's phone.
Either way, I don't see what you're getting at. The terminal is the phone in many cases, and other cases, there is a terminal in the sense of an integrated scanner system, but why does that matter? For the user it is much more convenient and faster. It's essentially instant, and I have never waited for the amount of time it takes for a credit card or NFC payment method to process. Further, it allows basically anyone to have this method because, again, the terminal is your phone and can be so for both parties in the transaction.
> And NFC works when my battery dies.
So what? You can charge your phone essentially anywhere in China.
By and large when I've used these systems, the vendor just checks they received the correct amount of payment in their app. It's largely immediate
China netizen population is estimated around 900 million. So essentially all adults in Urban and many in rural excepting small kids. Generally for the elderly, their kids or grand kids will help.
Pretty easy to fake a receipt.
QR codes seem to have largely supplanted cash and credit cards in mainland China, whatever hypothetical downsides they might have. And the very limited hypothetical advantages of NFC (it's unclear to me what they actually are, but let's grant they exist) don't compensate for the fact that an expensive terminal is needed, so NFC isn't displacing QR codes in the near future.
NFC terminals aren’t expensive - especially since they can be a cheap phone now.
QR without validating payment received is probably only viable up to maybe $10USD before the risk of being defrauded is too high.
I bet you’ll find lots of one way QR shops have a phone that they verify they’ve received payment on anyway.
And, yeah, most places do verify based on another phone.