No, it's the mark of "many people no longer carry exact change." An unattended box of produce and a sign saying "please pay this code" still requires trust that people won't take the produce without paying.

How is making it easier to pay (cash is not as commonly carried) a mark of a low-trust society? The important part here is that the roadside stand is still unattended - it's still up to the purchaser to purchase instead of stealing.

No, it's just a cash replacement, the trust lies in expecting people to make the payment in the first place rather than just steal unattended goods.