In reply to Jimbocz:
This has been my experience in a lot of places, yes. I have a Nationwide Mastercard which allows fee-free, commission-free purchases in shops and restaurants, I am probably still not getting the best rate I could. I've had it for years and it's been helpful in lots of European travel. EXCEPT IN GERMANY
Hotels are usually OK but quite a lot of restaurants and some shops are no good. I did quickly Google this and the broad view is that Germany is not a credit card culture.
Mastercard seems more accepted than does Visa, but then again I usually try the Mastercard first because my Visa cards will incur larger fees.
I remember last year when I was staying near Hannover for a working week, I stayed in a nearby spa town called Bad Nenndorf. One particular evening toward the end of my stay, when my physical cash reserves were getting low and I wanted to hold onto my last 40E cash in case of any cash requirements on my last day, I trekked about a mile checking 4 or 5 pubs and restaurants for my dinner, to see if they would accept AMEX, Visa or Mastercard. Nope. Ended up getting a cheap Chinese buffet, an hour later than I'd planned, in a deserted restaurant at the edge of this small town. It was all a bit depressing!