As a German a.) I mostly pay by credit card because it is way faster. By using paywave you can pay instantly at all larger shops and supermarkets. b.) The shops need to pay up to 1.7%. If you compare this against the time saved by not returning change and having to carry a money cassette every evening to their bank the saving potential is big. I try to not use cash anymore, but fail to do so in smaller shops or at the hair stylist.