Payment system using taler.net . No fees (except a tiny fee to avoid attacks on the system, and another fee in favor of the salesman, see below), but in a disagreement/dispute between two prices, the difference goes to the United Nations to help the environment. This difference creates a Carbon credit (in fact Certified Emission Reductions, by the United Nations), which is split in half to buyer and seller.
This creates a sink of money (just like taxes), which attributes value to a digital coin (ec0.in , with symbol ϕ). The ec0.in is produced by aidpla.net (which acts as a kind of central bank) and it can be used in payments where Carbon credits are produced. To preserve privacy, the Carbon credit is represented by a second digital coin (using Taler, we call it CER) which can replace ec0.in whenever someone wants, through aidpla.net.
The sale of ec0.in is done through the salesmen, who can (and should) charge a fee to the client, say 3% which also covers the costs of conversion from the local currency to ec0.in. The salesmen can also refuse to accept ec0.in for his products after a certain pre-determined (by them) limit is reached. The salesman can print a QR-code which is a certificate that says to the clients that this salesman has a good justification for not accepting ec0.in temporarily, until he gets to sell all (or most of) his ec0.in.State-of-the-art: engineering in the era of big data.
aidpla.net charges 20% of the fee that the salesman charges to the client, 1% of the Carbon Credit, and a tiny fee to avoid attacks on the system. That is, aidpla.net only wins when the salesman wins or when there is a Carbon Credit produced otherwise the payment system is essentially free (except for the tiny fee to avoid attacks on the system). Note that aidpla.net itself is non-profit, with all profits either reinvested in aidpla.net or buying Carbon credits from the United Nations.