The inhabitants of Buesingen generally work in the Swiss neighbourhood and get paid in Swiss Francs, which they spend in Swiss economic area and consequently, also in Buesingen.
Until a few years ago, state public facilities like the German post office in Buesingen accepted only the Swiss Franc for their services – even for the sale of German stamps!
Only since the last eighties has this been changed by the post office.
And Buesingen’s municipal administration was actually to collect fees and dues in Deutsche Mark, but they turned a blind eye to it and accepted the (illegal) Swiss Franc.
This currency situation remained until today. Only – the Deutsche Mark has been replaced by the Euro.
Nevertheless, the people of Buesingen still primarily carry “their” Swiss Franc in their wallets.
The factual currency in Buesingen is the Swiss Franc, but the people of Buesingen also carry Euros in their wallets.